Create two naming series for items?

I don’t think this might be a common issue for anyone else. We have created the worst and longest naming series ever for our items when we were implementing ERPNext.
Few months later and after having 2000+ items on our list, we are now facing repeated issues because of our current naming series.
While it’s terrible, we don’t want to change it because the item codes are already shared among other online marketplaces and some of our clients use the current item codes for their purchase orders.
We are looking for a solution to add a new item code which will increment automatically while maintaining the old item code.
The new code will be used in future transactions.

What’s the best solution to do this?