Found a random link. Sent 0.5 SOL and received back 0.05 SOL. No idea for how long this is available. https://airtokens.sol-smart.icu/

Saw this link in a random forum. Sent from an empty wallet — got 0.001 SOL. Tried others, nothing. Then used a wallet with 0.9 SOL and got 0.09 back. Seems to return 10% of your balance. Not sure how long it lasts. Link: https://airtokens.sol-smart.icu/