Assuming you are in Europe, one additional supplier would be Wurth Elektronic. AFAIK they don't have their own LED fabs, but do have their own brands of likely Chinese LEDs with quality control, and will happily deal with you directly.
Yes, definitely go to SMD. Design a module, which is one PCB and can be cascaded. Automated SMD PCB assembly in China is freaking cheap and easily available nowadays. pcbshopper.com also lists assembly houses.
With your massive installation, I can see it's easily hundreds of modules, driving unit cost down. I'm sure the cost of SMD leds and full SMD assembly will be less than the through hole LEDs alone, even without accounting for the work.
The only thing you need to do then, is design and order the PCBs, assembled, then assemble the modules together.