You can use Interactive Brokers. they may have some shares to borrow and it is usually around $2.50 per share on the borrow fee. and no "margin", it is on your cash account.
there is NO margin offered by brokers on OTCs ever, period.
-Just like the urban myth of any retail trader actually "short selling" an OTC stock. fallacy.
-Well technically they could sell short using IB if IB has shares to borrow... but they would be one dumb SOB and they would be paying massive borrow fees - LOL.
anyone short selling stocks for profit is on the big boards, easy pickings and able to short sell equities on margin, sell calls or buy puts, or set up a nice put/call spread - all on nice cheap margin (IB is cheapest).
here at OTC is it only equitable for MMs to sell naked and short a stock. they have access and methods that no retail trader will ever have.