You should be able to just get any high and low calibration fluid. It does not need to be Apex... Just as long as you know the correct data set...you should be able to calibrate any device with the callibration fluid.
I have a few packs of each. If you are in the city I can give you a 7&10 for 2 bucks.
I also have some if you like to stop out- lmk
I have the bottles from my reefkeeper but it seems you have several options much closer than I am.