First of all, a photo of the front of the recoil shield with the cylinder removed is a must.
Yes, it can be repaired but it will not be cheap. Shooting heavy loads in a brasser tends to imprint the rear cylinder ratchet into the frame. With hammer down or at full cock there will be considerable cylinder end play. At half cock there should be considerably less because the ratchet does not fit into the damaged portion of the recoil shield. A very thin steel shim washer the same size/diameter as the damaged portion of the recoil shield can be silver soldered in place so as to obviate the damage, but the barrel/cylinder gap will have to be addressed.
The arbor is steel and is pinned into the brass frame, the pin being visible when the hammer is at full cock. It can be drilled out, the arbor reset in its threaded hole with Loctite, and a new pin installed. Normally an arbor in a brass frame works loose during the ramming of the ball into the chambers of the cylinder due to excessive force using oversized balls.
High Standard used Uberti parts that were finished by HS in the US. Although marked Griswold & Gunnison by HS, it is nothing more than an 1851 Navy .36 with a part round/part octagon barrel. Since it was manufactured prior to both Uberti and Pietta going to CNC machining, internal replacement parts will be very hard to find if needed.
If it was mine, it would be a display item only as it has seen better days and not worth the money to restore it, and even if restored it won't be original. Prior to the pandemic, Pietta marketed a G&G .36 that is CNC machined and replacement parts were readily available. I have one but do not shoot it. I only shoot a few steel framed revolvers in my Pietta .36 collection.
Regards,
Jim