The Dynaco clones that Triode Electronics sells will work fine in your 200S. The original manufacturer doesn't really matter, it's the circuit requirements that matter. Sunn's early tube bass amps were based upon the Dynaco Mark III hi-fi amp. The very first "Smiley Face" Sunn amps were literally a Dynaco Mark III power amp with a small, 2-tube, pre-amp that was based upon a Dynaco circuit.
It's very fortunate that the old Dynaco tube hi-fi amps are prized collectibles (I have several myself, along with "way too many" Sunn amps) as this has made it economically feasible for manufacturers to produce these excellent quality reproduction transformers.