Hi Joe? and welcom to the forums.
There is a specific forum for RA saws, spindle moulders, thicknessers etc further down Woodwork Forums
here.
I have a B&D/DeWalt 740. The spindle on this has a hex key recess to hold the spindle fixed and a Left hand thread nut to secure the blade. While have all of the original kit for the saw, I also have a plentifull supply of handtools so finding a matching hex key for the spindle and combination ring/open end wrench for the nut is not a problem for me.
I haven't had enough to do with the Ryobi to know whether it uses similar systems, or has a push button spindle lock, or a couple of flats milled onto the shaft to lock it. However it is fairly likely that it uses a metric sized nut, so you would probably need to find a metric wrench (and hex key if used) to suit. These should be available from auto parts or tool supply places given the range of imported cars in the US.
Hope this helps.