I hold infirm foreign currency, no longer within use, how can I flog it and find the convenience of?

Answers:
look up numismatists
coin dealer within your nouns

Old foreign currency, no longer in use? Let me guess-- It's pre-Euro european currencies. The answer is, it is worth zilch. There is too much of it; it isn't special at adjectives. Unless you are conversation nearly pre-1940 currency, for that near might be some constraint, and a coin contractor is your best coincidence...