You'd want to talk to maverick74 about that. I don't think you'll find any web-reference, but there is a couple of threads on it here. vtradergroup.com is one. I believe Cornerstone shut-down last year.
Access to retail PM/risk-based haircuts have probably not helped to grow the niche.
G2 and First New York are the ones I know about. Also, in Chicago there are multiple places_in the style of Bluefin, which is more oriented toward market making.
Also, try Cutler group. We are a San Francisco based Market Making/Prop group with offices in San Francisco, Chicago, Philadelphia, and New York. I would be interested in looking at your resume. PM me.