Hi Kat,
I have not read your first post yet but shall. I apologise if anything I say below offends! That was not the intention.
You have my sympathy. And a tinge of envy. Why the envy (like I said, I have not read your first post yet). Even here on this forum, members have challenged my right not to want vaginal sex at all. Because I have a pussy, I'm supposed to put up with vaginal demands, so as not to be "selfish". I realise it would be different if I did not have a pussy (like a T-Girl), or could not use my pussy (even if I wanted to). It is tiresome having to explain my own normal to the ignorant.
The sympathy part is that, to be honest, there is no easy way to bring up the anal sex preference without a man instantly dismissing you as just a piece of ass, that he's going to tap, but with on intention of actually investing emotionally in you.
At least you are lucky in not ever having to go through the pussy route until you can cough discretely and ask if he's considered the other hole. Then hope he isn't going to recoil in horror at the suggestion. Or treat it as an optional (twice a year) extra.
My suggestion would be to raise the issue of not being able to have vaginal sex and leave it for him to come up with alternatives. The average ma will think that you giving him a blow job or hand job is a solution. A decent man will realise that you have no erogenous zones in either your mouth or your throat so expecting a blow job while offering nothing in return is neither fair, nor sustainable, if the lady has an iota of sense, or at least a little self esteem.
Jjust let it come from the man's lips, to suggest anal sex, when you tell him that vaginal sex is not a possibility. If the man has suggested something as "out there" to the normal world as anal sex, he will do some from a place of reverence, almost apologestic, probably half not expecting you to agree to it.
At this point, it is up to you to milk his "selfish" demands for all you can. Act as if you are open to the suggestion. Only later admit that you thought he'd never ask.

Don't let his narrow minded imagination run away with the visual of you giving your butt up to every man you meet because no decent woman admits to preferring anal sex. Only a truly anal-only man can still see you as a person to be respected after learning that you actually prefer anal sex (whether out of preference or out of necessity). Most men feel, and like I said, even on this so called "anal only lifestyle" board, that they shouldn't be barred from any hole. The pussy must be part of the deal. Only a really sympathetic man will take you seriously. And he may need to be coached on this.
There are cultures where ladies restrict sex to anal only, with the co-operation of their men folk, especially in communities where the ladies are expected to be virgins, and the penalty for not being a virgin (with the bloody evidence) can be a life-time of communal shunning as the bride that did not bleed. In those communities, the men don't assume the woman is any more a slut for having sex with her arse than he might assume if it were her vagina. It is not a big deal. There is a respectful understanding that the arse is a compromise for which the man is grateful. It's an open secret amongst the singles. But then, in these societies, you date with marriage as the long term goal.
As you are probably realising, in the West, probably no thanks to porn, the lady that has the nerve to say the A word first, is not the kind you take home to meet the family. She is typically only going to be good for NSA, or a pretence at commitment, until someone more chaste turns up. Her vaginal only counterpart that has a different anonymous one night stand every Saturday night, is more acceptable to consider.
But there are some men that can never consider a relationship without vaginal sex, but they won't be honest enough and will probably fuck your arse, to put it crudely, just to dump a load. Unless you are happy with such an arrangement and a string of one-hit wonders littering your emotional time-line, take your time and find out how consistent he is in his assertions that vaginal sex is not a must have on his coital menu.
Best of luck. Further down I thought I caught a glimpse of someone recommending that you walk around with a butt plug up you. But I must have read that wrong. Give me a second ...
p.s. I have been accused of being a man pretending to be a woman on here! That's the fair price of voicing an opinion in front of a misogynist. Being an anal only female can rub the most unlikely people up the wrong way.
kat wrote:So I said in my intro post that I basically can't have vaginal sex due to a medical issue, so I need some advice as far as dating and sex.
How should I bring up the idea that vaginal sex is not going to happen? When should I bring it up?