If anyone is looking for diaphragm pumps, such as for vacuum hold-down of flexible PVC sheet to press a phototool to a PCB for UV exposure, or maybe for spraying etchant, this eBay seller in Hong Kong has quite a selection.
I haven't tried it for a PVC flexible phototool hold-down system, but I think it would be suitable. I am only doing small PCBs and with the new small source UV LED light source, I am happy using glass with foam behind the PCB.
A search of eBay for "diaphragm pump" turns up 2,525 results and most of them are too big and expensive for this application: