Limaed, I buy the Theraband exercise bands on ebay, no particular seller but whoever is cheapest! The pockets I make out of scrap thin leather that I bought for making longbow grips.
There is a myriad of sellers who make up band sets for a reasonable amount.
Danny, I use 10 or 12mm lead balls that I make myself with those cheap ball moulds. I recently emptied out my airgun pellet trap and got several kilos of lead out which all went into the melting pot! I also come across bits of scrap lead on site from time to time.
Steve