Hopefully someone here will give you a specific recommendation, but if not, we can offer several possible sources to explore for anti-Cre:  https://www.linscottsdirectory.com/antibodies?q=cre%20recombinase

Select "Immunofluorescence" from the Applications filter and follow "more info" to suppliers' data pages.

anti-CRE recombinase (Rabbit Polyclonal, Covance, Berkley, CA; USA) dilution

1 : 2 000 000, yes million with ABC immunoperoxidase.  Our data suggest that it would work at 1: 100,000-200,000 for immunofluorescence.  We had purchased another antibody against CRE but it had no reactivity.  You might find this useful

As the article indicates, how you determine optimal concentrations will depend on the detection system, fixation, and tissue preparation.  Moreover, the length of time tissue is incubated with primary affects sensitivity (shorter times will require more antibody to detect something.  If using either frozen section or paraffin, you will need at least 10-50x more antibody to get staining. The high titer of that antibody is a plus when using less sensitive methods.  We have learned that staining can be enhanced with TSA amplification when using paraffin/frozen sections so you might consider using that approach.

Thank you for your answers.