Given that your check box formatted field is a match field in the portal's relationship, the simplest solution is to use Go To Related records. This can be used to pull up the desired found set on your report layout all in one step.
It is possible to set up a script to find the same records but it's a much more complex process. Your script would loop through the selected values and either create a different find request for each value before performing a find or it would find records for the first selected value and then use extend found set to find the other selected values. None of that should be necessary here, however.
Thanks for the confidence to go back to GTRR...I had tried it unsuccessfully a few times but after trying again and being a little patient, it finally kicked in and seems to be working as intended.