This one crops up quite a bit. (I'm basically reposting from an earlier thread. Might make an article out of it, it pops up so much. That'd probably be easier. As a disclaimer, I don't actually own any of these except for the
GW female Commissar)
There's a decent amount available, but it all depends on what brand of
IG you want, how realistic you want to be, and what you're willing to put up with.
Sure, realistically you wouldn't be able to tell a woman in decent modern armor from a man very easily, especially at that scale. But the
GW design philosophy certainly isn't about realism, and not too many people I know are in the hobby for explicit depictions of real life. There are other games for that. Unfortunately, a lot of the available options are a bit TOO exaggerated for many of our tastes, which leaves the market a bit wanting.
Official GW Minis
GW has done a few female
IG figures in the past. I'll draw pictures from dakka where available.
Female Commissar
Catachan w/ Grenade Launcher
Tanith female trooper
Warrior Woman and Rocket Girl (from the Last Chancers box,
still available)

Okay. Those are out of the way. There are a number of 3rd party manufacturers that make
IG conversion kits or obvious stand-ins. I don't personally think most of them are very good, to be honest, but I'll leave that for you guys to determine yourselves.
Replacement Heads
MicroArt Studios heads are pretty widely available.
Chapterhouse Studios do some female guard heads. I'm not a fan, maybe you will be.
Hasslefree Miniatures also make some heads that need some sculpting work.

There are probably other companies that do female heads. I'm not aware of any others off the top of my head.
Conversion Packs/Replacement Minis
Chapterhouse has a whole guardswoman kit out now, sans arms and weapons. They're kinda weedy though. I'm not really a fan of those either. They have posted some concept art of some new '
IG' models, although they've got a pretty modern look to them.
Concept art:

Shadowforge has two kits...I'm not really a fan of those either, but they seem to be the best of the bunch that are currently available. They also make some Catachan-ish stand-ins, as well as a couple alternative
IG-ish minis, all the way down to the cheesecake/skinamax sort of deals that really seem to go far towards advancing the role of women in miniatures wargaming. I'll limit myself to posting ones with shirts on.



TINs bits has a few conversion kits, but they don't have very good pictures of the assembled minis so it's hard to judge.

Finally,
Lost Clan/Phoenix Wargaming Club/Doc Thunder used to make a kit, but the purchasing options all seem to have dried up. Shame too, as I like these the best of the options out there. Still not perfect, certainly, but...better.
Miniatures of the North is working on some
IG-looking Redcoats which include a few female sculpts. They appear to be the most "realistic" of all the ones I've seen. Pretty nice. Not out yet.
Raging Heroes has a charming little Disco Commissar. Cheesecake, yes, but I find it ridiculous enough to kind of work. I might get one just for the back of the coat. It's pretty cool.
WarForge makes another female commissar. Less disco, but she's still rocking a corset and cleavage. That said, pretty awesome sculpt. I've got one of these on the way, personally.
Alternative Models.
Lots of companies make female minis that don't really fall into the
GW style, but could potentially be made to work. They are far too many to list exhaustively, but try looking into Urban Mammoth, Infinity, the Mantic/Hasslefree partnership, and possibly even Warmachine for a few select minis.