Hi Dawson, the problem with your sand filters might be that it is the top of the range and actually for large(commercial) pools and not really for koi ponds although you can adapt the fingers.
There is also a tendency to move away from pressurized systems.
It is fantastic filters, but because it is the top of the range, your market is much smaller. Maybe you should also advertise on Bid or Buy and Gumtree. The pool industry is much larger than the koi industry. Rather focus on the pool owners.
The pump is very reasonably priced although people with koi ponds prefer the lower wattage pumps and the 1.1 KW might put koi hobbyists off. Once again, this is a very nice pump for a large pool although quite a few peoplee run 1.1 kw pumps on their ponds. Koi ponds run 24/7, pools only run a few hours, and the high wattage would not be a big problem for the pool owner.
Where are you situated?