AFAIK, there is no such thing as a Swiss headset. Most older Swiss frames used French headset, newer ones English. One twist sometimes seen on Swiss frames is a French HS, but a 22.2 stem, meaning the steerer wall was pretty thin. English, Itaian and French heatsets all have the same pressed cup OD, 30.2 mm, meaning for a given model, the pressed cups are identical across those three threading standards.
Looking on the website created by the late great Sheldon Brown, it sounds like you need a JIS - old Japanese standard - headset. JIS has a pressed cup OD of 30.0 mm. Harris Cyclery, Sheldon's longtime employer, has two different Tange models of JIS headsets. Other CR-related shops may also have JIS headsets. I have no clue why a Swiss bike should have a JIS HS, but if it measures 30.0 and a 30.2 English/Italian/French cup is just a little to big, then I don't know what else it could be.
Be aware that JIS headsets also have a 27.0 mm crown race ID, whereas most ISO/English/Italian/French headsets had a 26.4 mm crown race ID, although 27.0 mm was occasionally used with these threading standards as well (except ISO). So measure the crown race size of the fork also. If it is 26.4 mm, you may have to buy two headsets of the same model, one JIS and one ISO, although somtimes one can use a spare crown race from a different make or model, provided that both headsets use the same size bearings.
Big Spring, Texas, USA
> From: Robert Goughary <email@example.com>
\r?\n> Subject: [CR] Headset Advice and need to buy asap...
\r?\n> To: firstname.lastname@example.org
\r?\n> Date: Thursday, May 21, 2009, 12:34 PM
\r?\n> Hi all,
\r?\n> i purchased a Cilo frame a few weeks ago from a seller in
\r?\n> Poland - frame arrived and has some bad road rash that was
\r?\n> unexpected - but it'll work fine for my "kick
\r?\n> around" bike until my other frame gets back from the
\r?\n> paint shop....
\r?\n> Anyway - Swiss Frame, Swiss BB - I have need for a headset.
\r?\n> It seems that my English nut screws onto the stear tube -
\r?\n> but the headtube inner diameter is 30mm (I don't have a
\r?\n> caliper) - so niether my english headset nor my Italian
\r?\n> Headset cups will fit in the headtube.
\r?\n> First - What is this? Swiss? English? French? Mixed? And
\r?\n> second - does anyone have a campagnolo or edco or Shimano
\r?\n> 600 headset (or similarly eighties appropriate) that would
\r?\n> fit- and that you would sell?
\r?\n> I bought this thing to build it up quickly - I need to get
\r?\n> out on the road - the weather in the north east has gotten
\r?\n> really nice!
\r?\n> Rob Goughary
\r?\n> Stamford, CT USA