Where to get Pandan extract?

If you live near an Asian grocery, you might be able to find frozen pandan leaves too. You could blitz those with some water to get an extract (that leaves a very pleasant green color to custardy desserts), or use the leaves themselves to lend food their fragrance. I agree with HalfPint that pandan and vanilla don't taste at all similar. I know the internet suggests you can use pandan like vanilla, but I think the internet is off on this one.

Your local Asian grocery store might have it. I would look in the aisle with seasonings and spices. If they only have the frozen leaves, you can make an extract with the leaves (search web for "pandan extract"), though this extract is best for immediate use.

Since you're looking for a substitute for vanilla, I would forewarn that pandan's flavoring is nothing like vanilla. True it is 'sweet', but in an herbaceous (it's a grass after all), almost woodsy way. Vanilla is sweet in a flora way. They're nothing alike (to me, anyway). Pandan can be very strong and almost overpowering.