first of all..welcome...i cant help you with the liner research but i think that a pump like that might be usefull for what you want to build.
http://www.ebay.co.uk/itm/Submersibl...ht_2795wt_1139 ... im not sure if u need a submersible pump like that or a pump that looks like this one --->
http://www.ebay.co.uk/itm/Eheim-1250...#ht_500wt_1128 ...wait for others who know better about pond supplies