Your hunt for a powerful water blaster is a common one. However, if you're looking for something also that you're likely to be able to acquire by this coming weekend, there are a number of stock blasters that perform well, though not at the level of the harder hitting classic CPS-series.
Current decent-performing stock water blasters I'd suggest for now while you keep looking for bigger ones include:
Water Warriors Orca
Super Soaker Arctic Blast + Max-Infusion Backpack (100oz)
Super Soaker Flash Flood + Max-Infusion Backpack (100oz)
Water Warriors Hydra Pak
While not as powerful as blasters like the Super Soaker CPS 2000 or CPS2500, these ones are available in many stores so are much easier to find. Depending on the typical user and blaster you'd find yourself up against, the above blasters should do well. If you're up against primarily small armaments, you should have no problems.
Good luck in your search and let us know what you end up deciding upon and how it all goes!
