Have any of you used a bike rack or some kind of trailer for a bike for your SUPS? Any suggesting where I could find them.

Try supwheels.com I have used this design in another brand that doesn't exist anymore and it works great but you do have to take care for it flipping in rougher dirt roads or ruts. There is something so cool about riding out to the surf if you live close enough or to access breaks far from parking. Can also use without a bike to save your back and arms.

www.thule.com/en-us/bike-trailers/bike-trailers-for-cargo

Reacha sport trailer works great.
Unfortunately, they recently were bought by Thule and the prices nearly doubled!
Ouch.

www.thule.com/en-us/bike-trailers/bike-trailers-for-cargo/reacha-sport-beach-_-10101404