Contact Ranch Products. I believe they supply the moonclips that S&W ships with their guns. Don't be afraid to buy a quantity of 50 or even 100. You will be paying about $1.00 per moonclip, when you purchase them in a larger quantity, and you can easily sell the extras. You might even want to place an ad in the accessories for sale forum, just to see how much interest there would be from other forum members.
I have to respectfully disagree with Photoman44, I have a Performance Center model 627 which uses moonclips. I think they are the greatest thing since sliced bread. You are correct in that the moonclips or even speed loaders will be cumbersome to carry when compared to speed strips. I recommend having the cylinder champfered to make loading really fast. Even though the cylinder of my 627 was champfered at the factory, I had it champfered a little more to speed up my reloads. Check out some of the you tube videos, to see how fast moonclips can be.