Try checking the Parts - For Sale or Trade
forum or if you can't find anything there, make a post in the Parts - Wanted
And should either of those fail, Ebay
is always a solid option.
If you're dead set on OEM, expect to pay about $15-$30 USD each (depending on the condition) plus shipping and possible import fees. Aftermarket (Depo) would probably be about $10-$15 USD each new, plus shipping and possible import fees.
Just be sure to buy bumper signal lights for an 88-89 crx, not 90-91, as they aren't the same size.