Yes, I meant what Joanne clarified (thanks!) - it isn't worth looking for an INSURANCE company that has transgender care or GRS coverage when you're considering an employer-covered policy, because the employer can override that for themselves.
If you're looking for an individual policy, yeah, that's different.

I don't know offhand of any insurance companies that do offer such a policy, but I don't *think* it would hurt to call and ask (since if they say "yes" they shouldn't punish you for wanting it), as long as if they say "no" you're not going to use them anyway. I'm not an expert and I don't work in insurance, though!
I do know one unemployed woman who's been trying to find an insurer willing to take her because she wants her wife and daughter to have insurance, and so far three have rejected her for being trans, baby and all. So you probably shouldn't call and disclose unless you ARE willing to walk away if transgender care isn't covered; if you're looking for basic health insurance first, you could risk being rejected outright.
For what it's worth, I have had zero problem with the insurance company refusing to pay for things it did say it covered. That kind of crap happens to people all the time, so this is partly just luck, but in the past 3 years BCBS hasn't been any more difficult with me about transgender care than anything else.
Incidentally, I also have a close friend who went to Kathy Rumer, and that doctor DID take insurance - Blue Cross paid all but about $2000 of it to the doctor directly. I mention it only because I think Rumer's an exception, but she's out there.