Just saying -

Being near a major military base, it's really easy to have poncho liners altered in this method. I seem to recall one store, now gone, that pretty much had these on the shelf. Also had liners with velcro or zippers to better use them as sleeping bags.

And to make ya jealous - My poncho liners cost me all of $6 each way back in Sep 81. The next week, Oct, the price went up to $18, go figure. I bought 10, sold 5, still have 3 floating around that I can put my hands on. Think the other 2 are at my parents house. And for antiques, the liners are still going strong.