People ALWAYS go missing when talk of money finally comes up. So many people are like "hey, this will be cool, sure, I'll sign up" because so many of these fall apart before actually happening. So those people just act like cowards and ignore the topic instead of just saying they can't afford it. It really sucks, but it happens with every group run of something.
My suggestion is attach a read receipt to 1 final PM. That way you at least know if they are reading it or not.
This may be a little out of my control, but I'd recommend only letting those who have paid/deposited with the project be able to purchase the Colt Python. Make it an exclusive of sorts to this project and rewarding those who have stuck with it. Just a thought.