A couple different options.
Remington made a 20 ga. camo set that is 13" LOP. Part # 19552. Not sure if they are discontinued or not, but there is a set currently for sale on Ebay. $130 new.
There is also a laminate compact stock set for $120
Here is a black compact set for $70
http://www.midwestgunworks.com/page/mgwi/prod/19551 Or, they made a black stock that is adjustable, with various spacers that come with it to go behind the recoil pad. Not sure of the part number for that one off hand.
They probably made walnut stocks in the compact or youth model as well.
One note also- the factory walnut stocks for the Lt-20 in good condition are in pretty high demand. Just sold one last week on Ebay for $265, for the stock only.