These are NOS factory Mopar synchronizer rings for your A555, A568, A523, A520, Transmission.  They are OE factory NEW parts.  NOT aftermarket junk made in China.  And yes there are aftermarket ones available.  If you want those, let us know, we can send you a link to those for $25/each.  But beware, I wouldn't install them in my lawn mower's transmission.
 
If you are having your transmission rebuilt there is about a 99% chance the person rebuilding it is NOT replacing your synchronizer rings (i.e.  this part).   Usually a "rebuild" is limited to new bearings and seals, - ***unless you specifically request they replace your synchronizer rings*** - which they can only do if they actually have them in stock - or can order from Dodge - NOS Mopar factory synchro rings. 
 
Funny thing is...it's your synchro rings that go bad 9 times out of 10 (and ***hence why you are having someone rebuild your transmission***.....so that your trans will shift smoothly after being torn apart and rebuilt) - a lengthy process you only want to do once.
 
We only have a very limited number of these and once they are gone, they're gone.   Price is for 1 synchro ring.  Best to order 3 or 4 of them if you are having your trans rebuilt.