Start with real estate clubs. Private equity lenders often are very active in them. The link for real estate clubs is http://www.creonline.com/real-estate-clubs/index.html
Also, check out CREOnline's forum on real estate financing. The link is http://www.creonline.com/real-estate-financing/wwwboard6/ind
Finally, here are the names of a couple of people who might be able to help.
1st Metropolitan Mortgage
Envision Lending Group
I've never used either myself, but I've heard good things about Acquisto and I know he operates nationwide. I know Rosov somewhat, have heard him speak, and he's very sharp. I don't know the geographic area he lends in.
At 55% LTV, your investor shouldn't have much difficulty finding a lender.
Hope that helps.