Hi Markimel
If your printer is using modern technology he should have a Pantone Mixing guide, whereby he can match your colour whatever form it takes either RGB, CMYK or any other.
I retired from the print industry 14 years ago and had used the PMS system many years before thet.
Printed below is an extraxt from the official Pantone site; maybe you would like to show it to your printer?
Spot VS Process Colour - Appreciate the Difference
Spot Colours
Colours created without screens or dots, such as those found in the PANTONE MATCHING SYSTEM®, are referred to in the industry as spot or solid colours. From a palette of 14 basic colours, each of the spot colours in the PANTONE MATCHING System is mixed according to its own unique ink mixing formula developed by Pantone. You probably mixed yellow and blue paint to get green in your youth. Creating a PANTONE Spot colour is similar in concept, but with the added need for precision.
The precision begins with the printing ink manufacturers who are licensed by Pantone to manufacture inks for mixing PANTONE MATCHING SYSTEM colours. To retain their license, they must annually submit samples of the 14 basic colours for approval by Pantone. Printers can then order the colours by number or mix it themselves according to the ink mixing formula in a PANTONE formula guide. A PANTONE Chip supplied with the ink and/or job ensures that the printer achieves the colour desired by the customer.
Each colour in the System has a unique name or number followed by either a C, U or M. The letter suffix refers to the paper stock on which it is printed: C for Coated paper, U for Uncoated paper and M for Matte paper. Also created without screens, PANTONE metallic and pastel colours are considered part of the PANTONE MATCHING SYSTEM.
Due to the gamut of the 14 basic colours, some spot colours will be cleaner and brighter than if they were created in the four-colour process described below. Spot colours are commonly used in corporate logos and identity programs, and in one, two or three-colour jobs.