One trick that works (at least partially) for the time being - go to the
classic site, then navigate to Administrator options > Registered Users. When the list appears, you will see everyone who had created accounts under the old credentialing system (at the least, I do not know if this list shows those who never had an account on the old system but instead only ever had an lds account). In the username column, those that are blank have transitioned their account to an LDS account. Those that still show usernames never transitioned their old account to an LDS account. I don't know if this means they just created an lds account independent of their old account, however.
I'm confident this does not give a 100% accurate picture of everyone with an LDS account, but it's insightful. At least you know for (hopefully) a large number of your ward, which should help you focus your efforts.