I'd call ALL the Pantera parts vendors since they get in wrecked and burned Panteras for parting out. I know of at least two that would fit your needs. While you're waiting, your three-piece seat can be simply altered to provide some seat rake. The rear bolt-on straps have holes; convert the holes to slots and add hand-knobs to the metric allenbolt heads, and you can change seat-rake, even while underweigh. I did this 20 yrs ago to our '72 L seats, and it's worked well, since I'm 6'2" and my wife who drives 50% of the time, is 5'4". So the seat position must change for driver comfort.