Depending on what you are doing with it, and if it is one shot deal or constant use, take a hard grinding disk to the 5/8" solid on 2 sides. Won't take but a minute to size some short pieces for the joint. How many joints like this?

Put your location in your profile. Maybe a member close to you could mill it or something. Aluminum cuts a lot like wood, so you may run it through a table saw for long pieces.

 

Need to fit 48 of these joints and already tried the angle grinder method on the 5/8 with verrrrry slow success. Location in Akron Ohio. I'll update that thanks

 

You could skim that bar stock to size with a table saw and fence.

Since they need to be short I'd skim about a foot, pull back and rotate, skim, cut off a piece and repeat.

 

Ditto the table saw.

 

We use aluminum breakdown frames that have a piece of Solid round as the connector

http://www.adorama.com/AEH408E.html...ml?utm_term=Other&utm_medium=Affiliate&utm_campaign=Other&utm_source=cj_1609763

 

does that round piece with the spring tab have a specific name or do you know where i can source those individually? thats what i had in mind originally but couldnt find anything

 

The round stock would be better than square for another reason. The round stock will place the point of contact in the center of the square tube faces, instead of the corners (which have a slight radius).
If you really need the very compact profile of the spring loaded locking pins afforded by the adorama kit, then you will need to go that route.
But, if you are just looking for a fast way to put up and knock down, you can use linch pins to secure the connectors. Linch pins have a spring loaded poppet ball that keeps the pin from falling out, and have a folding pull ring to remove the linch pin when knocking down. You should be able to cut your own connectors from round stock. If you have to buy a slightly larger diameter of round stock than the ID of your square tube, the same technique of table saw and fence can shave the round stock at 12, 3, 6, and 9 o'clock for a precision fit.
http://www.amazon.com/dp/B0058I1J7W...YV86QV&tag=pgmp-1603-97-20&linkCode=asn&creative=395109&creativeASIN=B0058I1J7W

The url I posted was just for illustrating a typical linch pin (if anyone did not know the term).