I might have some of them,
there's a picture of a 620 here:
http://www.tvhistory.tv/1949-Hoffman-620-12in.JPG
And my set that I thought was a 613:
http://www.vintagetvsets.com/hoffman.htm
If yours is blonde however I think it should have clear or tan knobs instead of red?
Edit: took a few pictures.
The first set is a 10" Hoffman, the second is a 12" set, third is a close up of the channel selector, fourth is the fine tuning knob and last is what I thought was a Hoffman knob but it doesn't fit my set correctly, maybe a different model?
Anyway as I said I think Red knobs would be wrong for a Blond set but maybe you can use these picture to help you find the correct ones, I'd keep an eye on eBay and also contact Mike Koste of "Gobs of Knobs"