If you want to maximize lift capability, the Land Pride PFL1242 at 220lbs are probably the lightest you'll find. They're made specifically for tractors your size, but even if you upgrade to a bigger tractor you likely won't exceed their lift limit.
www.landpride.com
Most other manufacturers start at 2,000lb lift and typically weight over 300lbs, the ones below are the lightest I've found.
Everything Attachments has the lightest 2,000lb forks at 235lbs, but with a 5 month wait.
Pallet forks designed for compact tractors or mini skid steers. Free shipping!
www.everythingattachments.com
Bobcat has 275lb 2,200lb forks.
Move bulky, bagged or palletized material quickly and easily with the standard duty pallet fork attachment. Adjustable forks load and unload, lift and carry, move and place materials around a variety of jobsites. A load rating of 2500 lbs. evaluated by Bobcat engineers who test the strength and...
shop.bobcat.com
Woods also has 275lb 2,500lb forks.
Standard Plus Versatility All Woods pallet forks come standard with a lifting clevis that has the same capacity as the forks for picking up loads with a lifting strap or chain. Durability Certified, forged steel fork tines for strength, durability, and long life. Easy Operation Full-height frame...
woodsequipment.com