That's interesting. In the book 109 F, G, & K Series by Prien and Rodeike there are four photos of 109F-4's with 20mm gondolas from 1./JG52 and 3./JG52.
I could have remembered a bit wrong too, it may have been shown to be extremely rare. You'd have to do searches on it, the discussions should still be around.
Which is against the production philosophy of the wartime German aircraft industry. 
Doesn't work really well for many British aircraft either.
Spitfire Mk IXs:
Spitfire F.Mk IX (can have either Merlin 61 or Merlin 63, "universal wing" with two 20mm, four .303s and no bomb racks, centerline bomb rack, has full wings)
Spitfire LF.Mk IX (Merlin 66, "universal wing" with two 20mm, four .303s and no bomb racks, centerline bomb rack, may or may not have clipped wings)
Spitfire HF.Mk IX (Merlin 70, "universal wing" with two 20mm, four .303s and no bomb racks, centerline bomb rack, may or may not have clipped wings)
Spitfire LF.Mk IXe (Merlin 66, "e wing" with two 20mm, two .50s and racks for two bombs or two rockets, centerline rack, probably has clipped wings)
Spitfire HF.Mk IXe (Merlin 70, "e wing" with two 20mm, two .50s and racks for two bombs or two rockets, centerline rack, probably has full wings)