I guess you already know it will be hard to get an exact match, so the goal is to get as close as possible. It's not easy because you kind of need to do 2 conversions too (from tint to 100% Pantone to paint!)
I have 2 options to suggest:
1) Use the Pantone book and select one of the Pantone that is on the same page as the main color at 100%. Sometimes, you can get a close match...if you're lucky.
I simply used a few swatches closed to the original one. It works well for a 50%. That's an example from Photoshop but you can simply use your Pantone book for this and go a few swatches up.
2) You can use the color picker tool on the tint, and find a close match using the Photoshop Pantone chart. The link below explains partly how to do it.
Mismatched CMYK Values
Here's an example:
I got the Pantone 713 result by using the color picker on the circle at 50%, and going in my color libraries of Pantone in Photoshop. Photoshop suggested me a close Pantone to match that CMYK value and it's a Pantone at 100%.
Additionally, since you need a paint color, once you'll be close to your "real" Pantone without tint, you can compare the 2 Pantone book together, if you have them.
Or you can again use the Photoshop library and select the other Pantone book you need for your paint, if it's there, and see if it fits. It's never going to be perfect but that one way to do it.
You can use this tool below to find a close match too but sometimes the results are horrifying. I think it's better to compare book-to-book if you can.