The below is not financial advice or recommendations, do your own research.
Because I wouldn't want to link directly to a provider, it's best you google "borrow to exercise options"
There are a lot of articles there discussing the pros and cons, including pointing to providers that provide loans with limited recourse should the stock become worth less than what you exercised with in a liquidity event. (Be sure to read all the Ts+Cs).
Of course, anyone fronting the risk here will take a big part of the upside should your options eventually become good, they have to both cover their costs on your transaction, make a profit, and cover the costs on all the loans they'll provide for stock that will become worthless.
