Roman Balance / Libra / Trutina questions

[P. Clodius Secundus]

Does anyone here have special knowledge or interest in roman weighing systems? My Father was out antique hunting and he found me an old iron two-pan balance. There weren't any scale weights with it. I'm looking for examples of weight sets that I can copy.

[D B Campbell]

... an old iron two-pan balance.

The Romans (as far as I know) used the steelyard, rather than the (Greek) two-pan balance.

Using a steelyard requires only a single counterweight, which moves along the bar to achieve the balance (rather than adding more weight to a pan). The counterweights are usually highly decorative, often in the form of a bust.
Example from Daremberg-Saglio.

[Medicus matt]

The Romans (as far as I know) used the steelyard, rather than the (Greek) two-pan balance.

Not exclusively. Equal arm scales have been found in 'Roman' contexts (the lovely set shown below is in the Petrie Museum and is from mid 4th C AD Egypt and, as such, is possibly down to Grecian influence but I've seen an example from Pompeii that is pretty much the same).
Some combined elements of both forms, having two pans, an equal arm AND a small, moveable weight on one of the arms to make fine adjustments to the weigh at one end.