I've done some "research" on this in the past, and sadly I don't think you're going to find anything that will make you produce any more precum than you already do.
It seems you're straight, but one solution to not producing a satisfactory amount of your own is to hook up with someone who produces a lot of it and just connect with it that way.
Precum tastes ten times better than cum does, at a minimum, and it's always fun to suck someone who leaks like a broken faucet...