Speaking from experience, low-dose opiates, long-acting benzos, or maybe a spliff, would be your best bet (can you obtain green?). Ive found stimulants to obstruct my ability to communicate with people I'm especially nervous speaking to. My advice is to take it easy and think of whatever you end up taking as a tool, but not as an improvement to yourself or the way people see you. I often subscribed to the notion that stimulants and fun drugs would loosen me up to a degree where I felt safe and comfortable around someone new, but without fail, every time I think it will help - it does the complete opposite. I end up making a jackass of myself.
As the drugs wear off, the irritated self comes back, which doesnt help the situation for a date. Stims will never substitute because your attention is on so many other things as well.Its taken years of finding a balance that works for social situations, but being super-talkative the first date, and then less so each subsequent time just makes it seem like you lost interest. I cant say if thats true or not, but it's how I'd feel if I was on the other end. I totally sympathize and can relate to your dillema however.
Edit: You know what? Try a low dose benzo, followed by a small amount of amp.