Check with some of the regular boat movers. Some sell them new for $75 each
and then buy them back for $45-50 each when they come back to move the boat.
If you catch a boat mover who is willing, he my have a back yard full of
them.. You could also try the boat yards. The purchase them by the dozens
and if business is slow, they my have some spares..

You could build them but I have done the math and even with my own welding
and metal working equipment, it's not worth the effort.

Good luck

Steve
s/v Good Intentions