You should be able to purchase a single jack from Lippert. Usually, the BAL brand jacks available at RV dealers and Camping World are sold in pairs, so you'd have to buy a pair unless one of the places happened to have an extra somewhere lying around. Might just take a quick phone call to some of them...
There's also a company, Cuches International, who gives a discount to members of this site, and they sell jacks. I don't know anything about the product to know how it is, but they do give $5 off.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR