What about perhaps advertising for a roommate in an LGBT paper, I remember seeing ads like this in the Washington Blade, I assume it would work or people wouldn't bother paying for ads (I assume they pay since the Blade is given out for free lots of times near my old Metro stop, and they gotta pay for it somehow). Now, if you are worried about someone getting your number just buy one of those ultra cheap prepaid phones for $20 and use that number.
In an LGBT newspaper it shouldn't be a problem to mention being transgender, in fact I would mention it because not every person in the LGB is fine with the T.
That being said all of that only really helps if you even have a local LGBT paper. Not every city does.