I have one myself, you can refill them and it makes an awesome squirtgun!
However, I went to the local fire suppression systems company to talk to them about using it as intended. They have a guy who's been in the business since those squirters were new and he flat out says they dont make a equivalent type of fluid for them. The kicker is the need for some sort of corrosion inhibiter to keep the water from siezing the guts up.
