On Sat, 3 Oct 2015 07:31:55 -0700 (PDT), Tim
wrote:

This is a nice sumple old boat and I don't want to "restore" it but the plexiglass windshield is gaily yellowed. Anyone know where to get a replacement. Probably be worth more than the boat. Lol!

It might buff out with a fleece wheel and very soft buffing compound.
There are custom lexan fabricators who can make just about anything
but it will be a significant part of the $400 you paid for the boat.