Just increased the size of my rink to 40'x70'. Any recommendations to buy liners in the Boston area,preferably south of Boston?
When I used to build a backyard rink, I would buy my liners at J. Freeman. I had very good luck with them. The plastic is designed to shrink wrap boats, but it makes for a fairly durable liner.
I hear you. My rink was originally 32' x 64' and they had a liner that was 36' x 70'. The length was long enough of course but it could have been a little wider. So I cut a foot off the width of the rink to 31'. In other words, I sized my rink to the J. Freeman liner. You might have have to do the same if you want to use their 36' x 70' liner, which is $194, a big price difference. But like a lot of things, bigger is better when it comes to hockey rinks.
I did try the common sheet plastic that you can get at Home Depot in large rolls. But the plastic is junk and is prone to tears and holes. That is why I went with J. Freeman liners.
I don't know how you can do 40' wide. I've been using the 40' x 100' rolls from Home Depot for the past few winters. The 6 mil roll was ~$165.