The hard to find stuff for the 556.

Try Train Tender (Jeff) or keep a look out on ebay., Frankly, those are just sheet metal, you could cobble the frames from some thin tin or brass until you locate originals.  Lots of options.

i too recommend Jeff he is a tremendous helpful guy. He is looking for me. I have a couple gilbert lead casters and if i strike out too much i am thinking of just casting lead ones seeing it had a lead weight to start.

Doug Peck of Portlines Hobbies has complete repro pilot and trailing trucks for the 556, 565, 553, 545, etc. if this will help. Doug is a good source for many prewar Gilbert bits.

Bob

The sheet metal  front truck is shorter wheelbase than the cast one form the K5, Hudson, and Northern just FYI.  And I think I tried to use the longer cast one and it was too long, interfered on the corners etc.  You may have different luck though.  I think the cast K5 trailing truck side frame sides hit the bottom edge of the 556 cab as well.

Followed advise with portlines. Did have the 556 items i was looking for. The bad thing with part buying is no standard # that i know of. i know many units share the same part or a tweaked version there of .

Lead and trailing trucks also used on the 565 Atlantic and the 553 Grey loco.  The trailing truck is used on the 545 which is the four drive wheel version of the K5.