By "RuneQuest", do you mean Gloranthan? I have been collecting quite a few Gloranthan oriented miniatures. Here are a few to start with.
Lance and Laser and Ral Partha (now Ironwind Metals) produced some of the original ranges. Some more can be found at RuneQuest - Lost Minis Wiki.
Ironwind Metals has some good ones, including Rhino and Buffalo with riders, but I am unable to find new releases for most of the Gloranthan ones.
For "unofficial" Gloranthan miniatures, here are a few possibilities...
A good reference site is Gloranthan Army.
Mega minis (both cheap and good) - most US $1.50, with plenty of others to look at on their EBay store:
Beastmen RAM with Halberd
Beastmen PIG shaman
Beastmen RAM sword & axe
These 15mm miniatures make excellent Durulz for 28mm scale (if you are that way inclinded):
Duck and Cover.
For some Aldryami with a difference (or more to the point, not your Tolkienesque elf):
Twiglet One and Twiglet Two.
And some potential Yelornans.
Reaper Miniatures make a good and interesting range:
- Reptus are potential priest dragonewts (I prefer the original's for crested and beaked).
- Someone from Prax.
- Shaman a plenty.
The Fantasy range from ShadowForge has a good range of potential Sartarites, Yelmalions and Praxians (although all female).
For Uz; if I cannot find the 'original' type, I use Orcs and Goblins made by Inquisition Miniatures.
Games Workshop make a good number of "chaos beastmen", once they published RuneQuest, the never looked back. However, cost may be a factor.
Otherwise a "RuneQuest" search on EBay every now and then finds some good results.
Let me know if you are interested and I will find a list. I suffer from the problem of it being easier to buy more miniatures rather than paint them...
Edit: I am on the look-out for 28mm Zebra, preferably with saddle. Stripey horses do not have the right look.