If you cannot find a lab to do this, ask that your lab not cut the film
Then do your own final rinse, and hang the film to dry.
An approporate rinse is photo flo wetting agent, diluted to about half the recomneded amount in my experience, with a few ml of Formalin added in.
Trying to source Formalin, a 37% saturated solution of formaldehyde in water may be a challenge.
The other option, also challenging, is to source paraformaldehyde, which I understand to be dried formaldehyde, or at least is an analog to Formalin once it is in solution.
The lack of a Formalin rinse will not be an issue if you attend to it a few days, or perhaps weeks afterwards, if the negs in the interim are kept in a cool dry place. Being kept dark may help also.