Southco Swell Latch Repair

Where can I buy replacement rubber pieces for Southco swell latches?

The swell latches are used to attach windows in a sun room After 15 years the rubber pieces that should swell are rigid. I need to repair 72 larches but don't want to pay $10.00 each. I just need to replace the rubber piece which is 1/2 inch in diameter, 1/8 inch wall thickness and about 1/2 inch long.

Any suggestions?