Prismatic makes good stuff. I ran a production powder coating shop for almost 20 years and used that supplier regularly for specialty colors.
RAL 5018 is a color that many powder suppliers would offer. The RAL series (RAL XXXX) is pretty well standardized within the industry. There are a few RAL's that will vary slightly in color between mfr's, but in my experience blues like this haven't been a big problem. Many suppliers sell the RAL stuff in small quantities too, so you don't end up paying for a bunch of powder you can't use. I mention this because if you take your stuff to a production shop and tell them you're looking for RAL5018 they'll know what you're talking about and may have some on hand, or at a minimum will know where to readily obtain it.
Two cautions:
1) Check the supplier's data sheet to see if clear top coat is recommended. In my experience the main stream supplier's RAL's do not require a clear top coat. If it is required, that stuff is more difficult to spray properly and typically is either high gloss or low gloss. Either will change the appearance of the base RAL color somewhat. This leads me to item 2:
2) Most RAL's are made in about an 80 gloss, which is a bit higher gloss than the Mopar color you're shooting for. I'm going on memory now, so be warned, but I believe the Mopar turquoise was in the 40-50 gloss range. Higher gloss will change the way the eye perceives the color, so it will appear to you to be a slightly different color.
If you're trying to visually match colors, don't do it indoors unless you have a light table, which some coaters might have in house. Sans light table, your best best is outside on a reasonably sunny day.
Hope this helps.