Out of curiosity, is this company coming to you because they'd prefer giving you the business versus whoever used to do it, or are they coming to you because they can't get the product from their previous supplier?
I say that only because I've had to help customers re-standardize their graphics when another company shut down or just started putting out crap at outrageous prices. We tried as hard as we could, but couldn't get a 100% match for our new customer. So we found the best we could - and sometimes even improved their product for them. It took adjustment on their part, but over time it became the new normal.
We've also lost some potential jobs in the past because we couldn't figure out how to make a 100% match, so they stuck with their previous supplier.
Best scenario is you can find an exact match. But is it possible to shift them over to a new prismatic if you can't find that one?