Pandan extract in small quantities
From the recipes I've seen, it looks like the pandan extract tends to be made from fresh leaf and water - essentially it's a juice.  This might make it easier to substitute rather than if it had required other ingredients or preparation, use of alcohol or other solvents.

So, it looks like the pandan paste is the nearest substitute - the recipes look like it can be made from pandan leaf and water, it is just blended and kept - simple straining should make the extract.  Of course, commercial processed paste may have preservatives and stabilizers and such, but it might be workable anyway... or perhaps you can find a good product with few of the extra additives.

Another alternative is to pick up pandan leaves - frozen ones are available, even online, though it might take some looking, extra charges in shipping, or something like that.  Fresh might be available somewhere, but it's likely harder to depend on and will perhaps take more work.  Frozen will work for most applications - especially since freezing usually helps with extracting juice (extract, recall), will store better, and will perhaps be easier to find.

If you're using the dried leaves, you can soak them, boil, essentially make tea.  The flavor is weaker, and you will need more to get the same flavor, but since the dried leaves are just pandan - you should be able to reconstitute the leaves and extract the flavor the same way.  Dried pandan is available as a tea, it just takes a bit of looking.

As for the pandan extract, the advice I found was to buy the large cans of good, pure extract, and portion it off (like ice cubes) and freeze.  It will store well - at least as well as frozen leaves - and it will have just the pure flavor, so more flavor for the same amount of freezer space.