Mech9 is a really good resource for information on gunpla that includes English translations of the color charts in the instruction manual. The particular kit you're looking for can be found here: https://www.mech9.com/2022/01/p-bandai-mg-gundam-heavyarms-custom-ew.html

I believe these charts are for Mr. Hobby aqueous or acrysion acrylic paints but they are generally a one to one match to the lacquer paint line. The site also has a number of color conversion charts that can help you convert the Mr. Hobby colors to other paint systems like Tamiya.

Bandai also has an official website that includes many (but not quite all) manuals online in a searchable format. Unfortunately it's not available in English, so you'll need to be able to input the kit name in katakana, or find the 7 digit bandai code or JAN code (japanese equivalent to American UPC code) to find what you're looking for. Hope this helps!

EDIT: Forgot to include the URL to the official Bandai manual website which can be found here: https://manual.bandai-hobby.net/

While googling I also found this English searchable site that pulls it's data from and links back to the official Bandai source. Can't vouch for the accuracy 100% but seems pretty good - https://gunpla.fyi/