I've been looking into 15mm (so a jump up from 10mm) because it lets you do rank and file and "big arimes" in a way that 28mm just can't really achieve (at least on a sane budget and time scale). Note that with this scale the rules are fairly interchangeable and what works for 15mm can work for 10 or 6 quite easily and vis versa
A few thoughts/model lines that might interest you:
1) Battle Valor - makes some really great 15mm models. They've certainly got a large and diverse (and ever expanding) range so might suit for filling in gaps or providing a core, though they are at the upper end of the 15mm scale so might not suit if you're dead set on sticking to 10mm models
http://www.battlevalorgames.com/battlevalorfantasy15mm.aspx
2) Microworld Games. Yeah so after a 15mm suggestion this is a 6mm suggestion, however the sculpting is again really great
https://www.microworldgames.com
Might be another range to consider. They do offer 15mm but only one army thus far
Ps their website is giltching a bit for me at present, it might be a local issue or just a short term thing