While it would be great to search using a transaction id, I haven’t found a way to do so using Steemit condenser api (the current functionality is simply deprecated).

This is due to (the first history variant of) rocksdb not supporting this index. Mira full nodes will eventually be able to provide this functionality.
I have my own indexer for transaction ids that you can use. It follows the format of my RESTful converted apis with the call structure, i.e.,
https://anyx.io/v1/account_history_api/get_transaction?id=