go to the cheapest Dollar store type of place around you,,,,,get a box of sealable sandwich bags, cut into squares slightly larger than your lid diameter
you will now have a stack of squares that will let you seal glass paint bottles the same way that chemistry students do,,,,,except you will have to capture the plastic sheet (they can stretch their sheets over the bottle without a steel cap)
then, find old style plastic soft drink lids from Pepsi company products (new lids since Nov 2011 no longer work), those double seal on MM bottles
Lifecolor and Talon acrylic lids will both swap onto MM/Floquil bottles also,,,,,both have a "permament seal method" in their lid design, LifeColor is molded with a sealing ridge, Talon has a "sealing cone" part in the lid
sandwich bags work better then wrap, because they are slightly thicker, I have had both saran wrap and aluminum foil cut off around the bottle rim and fall into the pain
hth
Rex
edit to add: If you say "but, I don't want to spend half my remaining lifetime collecting LifeColor lids",,,,,,then just get half LifeColor and half "glass bottle brand" paints,,,,,,you will have some that are easy to get open because they are plastic lids on the glass bottles,,,,and some that are easy to open because they plastic bottles with steel lids with a liner,,,,if using steel lids with a liner, get the thickest clear plastic bag product you can find and cut lid-fitting discs out as inserts