Hello, Chwat! I am unsure if there are any online stores for pc games out there where you can purchase a digital copy of Battlefield Vietnam... I know Steam doesn't have it, Origin too as far as I know.. As for me, I bought my CD copy in local store long long time ago. I'm sure you can find a lot of sell suggestions for used and new ones on Ebay, Amazon, etc.
If I understand you correctly, the only reason you can't get in the game is the absence of CD reading device? I'm sure in our modern times there are a lot of cheap or even free options of obtaining one I hope you will overcome these obstacles and join us in this great game soon!
But don't forget that installing a clean game is not always enough, for more info check our guide here: Files & Guide