For information about this, Google "securities lending fully paid", that exact phrase. I don't know if Ameritrade has such a program. Fidelity and Schwab definitely do; you can call them and ask about it (use that exact phrase).
If you have a current Schwab account, the offer pops up as a fairly small link between the headers of the webpage and the contents, when you're looking at your positions list. When you select it... well, uh, the first time I did it, it basically said "please fill out a paper form and mail it back".
Anyway, once I did that, then the link listed which stocks they were interested in borrowing. They will only do it for stocks where there is huge short interest, so much that they can't get enough shares to borrow for free -- TSLA's the first one I've ever seen it with because it's never happened to any of my other shareholdings.
If you're actually using margin on an account, you will never get such an offer because if you're using margin, they can borrow your shares for free. At some brokerages this may be true even if margin is authorized and not used, but not at Schwab.
A fine point which might be tripping you up: Whether they can borrow your shares for free is determined by whether there's any use of margin on the *entire account*, so if you borrowed against some other stock in the same account, they can borrow your TSLA in that account even if the TSLA shares are fully paid.
So if you're using margin and want to get this offer, move all your TSLA and SCTY into one account with *no* margin borrowing (you can even call them and remove the margin feature from that account) and do your margin borrowing in an account at a different brokerage which doesn't contain TSLA and SCTY.