Where Can I Find Earnest Money?

I've found some great real estate deals that I'd like to get under contract. I know I can get the financing, but I'm not very liquid right now and need about 50k to tie up these properties. What would be the best way for me to borrow this amount for refundable earnest money? Which type of lenders are open to this, and how long does it typically take to get the funds? I have about 3 weeks at the most.