OK. Oerlikon as in the much used 20mm WW2 Allied AA gun? Commonly used aboard navy vessels? That Oerlikon?
If you just want the barrel assemblies and fancy scratch building the rest yourself then Gasoline/Quarterkit do the Polsten barrels for a conversion of Tamiya's Crusader SPAA kit in 1/48. That's possibly your cheapest option.
There is to my fairly certain knowledge a 1/48 Oerlikon kit available from a US (?) company that produces ship fittings for scale models in various scales. I remember stumbling across it about a year ago whilst looking for a similar item. Sorry, I can't recall the manufacturers's name and I was daft enough not to bookmark the site. Try googling 1/48 Oerlikon.