@aldrahill
Here is what I’ll say.
I am in a similar boat (I have G40, 41, Risk and D-Day) and I think my way works.
I use a form of RC’s chip method, marking pieces with chips to designate their function. This eliminates huge numbers of sculpts.
I use risk pieces as militia, calvary and coastal guns, and then I made clay fortifications. any other bases I use other clay pieces, or G40 markers.
For the CCP, I use Russian pieces, and the KMT French. If the bigger power comes, I would pull out more roundels to mark. Similarly for Spain. (that time USSR and Italy)
For Vichy, I just use vichy roundels under the ships and on the territories, and it saves you from getting another set.
For the neutrals, I have a few neutral infantry from when they were cheep, but I mostly leave the off board until needed. Then they are aligned, or if controlled, just use an upside down roundel and the controlling powers pieces.
As for a bundle, I know that HBG used to do a buddle for their original 1939 game, but stopped because not many people got it. Either the high price or imperfect nature of what was in it, etc, drove the awway. I am sure if HBG did do one for v3, then they would have tons or pieces, but even then, not they don’t have everything. Some things you would need to paint or outsource, and it would be prohibitively expensive.
Also, here is GHG’s list of needed pieces. Some errors I know of are a need for more light cruisers for the US/Japan, or more seaplanes (6-8?) for the Commonwealth. Also, France and Anzac could use some tech units.
Note: This is ideal. Not needed. IF you have less, you can probably still play the game.
https://www.historicalboardgaming.com/assets/images/HBG/GW1936v3/Accessories/Needed Units for Global War 36V31.pdf
I hope that helps.