If you're getting BBBJs (bare back blow jobs) and you want actual sex, aka full service of FS, then just ask. Ask however you want, say "ok I wanna fuck you now," if you feel like it. Have a little fun, she's not gonna bite, unless you ask her to.
As for condoms, I always bring two with me. In the past I've had the girl run out or they don't have my right size, so I always bring my favorite brand with me. This will avoid the girl going "oops I ran out, we'll have to stick to blow jobs." or the thing slipping off because it's not fitting right.
I mean, is that the issue? You can't get past the blow job phase because you're not sure if condoms are available?
In addition, you seem too timid. Just tell her to stop giving you a blow job and that you want to do something else. Be a man and take control, what's the point of sex with hookers if you're going to be timid about it? And always, if your provider is not providing the services you're requesting, you always have the option of moving on.