Hi if you are sewing leather on a regular sewing machine you need a size 18 needle. You also need a walking foot with grooves underneath so the leather could move freely when being stitched. In terms of thread you need #69 Nylon Thread-it is strong and durable on the leather. Normal thread could work but it might burst easily. Normal thread, if you take your time, could work on light suede. You also have to adjust your tension and stitch length on the machine-I suggest you practice with a scrap first.
With regards to where you can get leather-it all depends on where you are located. I am in New York so I could tell you about places there. You can also check ebay they have a lot of sellers who sell leather and scraps. Leather is sold by the square foot and prices can vary a lot. Leather is usually expensive.
You can sew that wrislet you just have to know what you are doing since leatherwork involves certain tools, glues and techniques to give it a professional look. You can PM me if you like-I study Accessory Design at FIT in New York and I take handbag construction classes in leather.
From here onwards these are suppliers and some are international. Yahoo search word "snap suppliers" "colored snap suppliers" The word "supplier" makes a major difference to find what you are looking for.