look into automotive paint dealers / distributors.
a good coat of adhesive promoter & a couple coats of a good automotive dye "should" hold up to a motorcycle seat.
if you have ever seen paint chip books? like when you paint a car... well there are color chips to buy automotive interior dyes too. many body shops use to match parts, & the good dyes seem to hold up well.
if I was going to change color I wouldnt hesitate to use the automotive dyes. it may still rub off in high wear area, but a recoat would be applied.
the only down side is you need an automotive paint gun & compressor to apply.....
might be possible with a wagner power sprayer on the cheap? but when I went to college a guy bought cars at auction, sanded with electric sander, & painted with a wagner power sprayer, using house paint, he paid his way through college for 2 years, plus his gf, just reselling cars with new paint jobs. his only compressor was a small portable hand held.
Later,
Randy