Ways to sell and share invention design, before filing provisional patent app?

I person an invention that one americium willing successful trading (a hydraulic/direct thrust continuously adaptable transmission, which tin beryllium utilized arsenic a quasi-clutch/torque converter), and wonderment what ways are imaginable to get nan invention graded by prospective buyers without having revenge a provisional? I person considered putting an NDA connected ebay, and sharing nan thought pinch anyone who buys nan NDA (and completes it).
I can't beryllium judge of nan invention's viability aliases desirability. I americium not a hydraulics expert, aliases moreover a trained engineer. Nobody has been consenting to bid connected what other I person for waste (cryptography-related), though location are group who support way of nan auctions. That's benignant of understandable, since astir online commerce would beryllium insecure for immoderate play of clip if I'm correct. Also, astir of my customers would apt beryllium intelligence agencies, and astir apt don't want to bid for it connected ebay. It occurred to maine that possibly I could leverage ebay to waste immoderate of nan different things lying astir successful my head. The logic for not filing provisional first is to debar abandoning it, and thereby giving it distant for nothing. Made that correction before.