How can I proceed with my EB-5 I-829 process if I do not have my conditional permanent resident card?

It may be advisable to file for a replacement card and explain the green card was damaged-you can likely take a picture of the pieces and explain this when you are seeking a temporary green card stamp.

Yes, file an I-90 for a replacement card.

By regulation, you still have Conditional Permanent Residency even if the document itself has been destroyed (in much the same way as you would remain a citizen of your passport-issuing nation, even if the physical passport were destroyed). As long as you have a properly filed I-829 and receipt notice, you have Conditional Permanent Residency status, and your CLPR document is extended automatically for 48 months beyond the printed date of expiry. In order to replace your card, the usual process would be to file a Form I-90. However, sometimes the USCIS internally seems to be confused by this, and may respond with "but your CLPR card has expired and cannot be renewed." This is where an immigration attorney may come in useful, to provide legal explanations to USCIS about why the holder still holds valid CLPR status and is eligible for a CLPR card that reflects the actual current valid CLPR status of the holder pending I-829 adjudication.