For film holders ebay is my choice. I try to get them in multiples of 3 (and load them in multiples of 3) because that equals what can be loaded in a Jobo 2521 with the 2509n spiral that holds 6 4x5 sheets. I find the Jobo easy to load, but in a changing bag it gets tight. Uses a lot of chemicals when doing manual inversions but when using rotation one-shot is possible. Other option is a Paterson with the MOD54 spiral (also takes 6 sheets).