The SailNet store carries Lewmar hatches. Size 60, which is 22 11/16 x 22 11/16, possibly the size you're looking for, is listed at $398. Here's the link: http://shop.sailnet.com/product_info...oducts_id/3924
Although I have not worked on Lewmar hatches, I did build 6 new hatches for my boat in 2003. If you use Boatlife Life caulk, as recommended previously, and you're careful, you can probably replace the lexan (or use cast acrylic instead of lexan) yourself and have a leakproof job.