Most of the big startup law firms will take clients, usually with some sort of referral / partner interview, on a fee deferred-fee basis, especially now. They give you up to about 5k worth of legal work, which you have to pay if you raise money or generate revenue. If you go bust, they just write it off.
Off the top of my head, check with Gunderson, Cooley, Fenwick, WSGR, etc.