You don't need a disk to align the saw, a length of flat iron with a 5/8" hole drilled in it works just fine, measure it at one end of opening then flip it over to opposite end, which is actually no different than measuring from the same tooth on a saw blade.
This is not "rocket surgery" and there is no need for sensitive measuring devices, just a good sense of touch and patience.
If you can find hardened washers use them, otherwise buy new ordinary washers they will be fine the first time they are used, just don't use the original washers.
They are nice to have regardless, since they can be used for accurate sanding of miters using a miter gauge as well as aligning the table saw blade. They are NOT cheap, but that's because they are precision ground I think to 0.002", but I won't swear to that number. Somehow I ended up with two of them over the years.
Those older members may remember niki who was a wealth of information. He posted this in this thread I started:
I also use this method....but, as the others said, it's "almost"....
By extending the blade line to 24" (in my case 30") and checking the distances at the ends of the straight edge, you can minimize the error (misalignment)....well, instead of measuring the error (misalignment) over the 8"~9" of the blade, you are multiplying it a lot by checking the error over 24"...
You can see one example here
And another example here
Please note that in both cases, I'm lifting the straight edge off the table (to cancel any drag or binding) and, I'm using a caliper for better accuracy......and I think that if you get some 0.002"~0.004" on the 24", you are good to go...on 8"~9" of the blade, you'll get much less...
I call the above adjustment/test "Static Check"...
After I finish the "Static Check", I like to fine tune (or fine test) the blade using the "Dynamic Check"...yes, yes with the blade running at full speed...with the "Dynamic Check", all the Arbor run-out and the blade run out (and every blade has a run-out) are already "Included"...you can see it here
By the way, all the checks/tests should be done with the blade a "Full High" position....correct me if I'm wrong but, on the pictures, your blade doesn't look to me at "Full high"...