1. ucla extension classes did okay for me; you just pay & take classes and I got into a few schools
2. i know of someone taking postbacc stuff at usc - but it's crazy expensive
3. scripps has a formal program - but you have to apply & get in
4. yet another friend took a combination of ucla ext. classes and others at smc (santa monica college) (and he got into ucla & ucsf - he had very good scores)
one footnote - my friend and I are unique candidates - we're both old & changing careers so our apps looked diff from most.
I remember looking for the same info you were & found some random websites & lists of urls. they're out there...
good luck!