As a Viscount owner, I can advise that this can be a tricky issue. It is worth of persevering though as these bikes are quite unusual now and very nice to ride and I consider them very under-rated.
If you can't find a suitable chain ring in the correct BCD (try SJS, they have a lot of oddities), then you will have to replace the chainset and this is where it can get interesting. Your bike probably has a pressed fit bottom bracket bearings. These bearings are cheap and easy to replace if they are worn despite what some might say.
The bottom bracket axle is different from the norm as it is straight with no bearing surfaces. Is your current chainset the square taper type or is the almost unique to Viscount square fitting without the taper? If it is the tapered variety, you should be able to use any other standard square taper chainset if the width is correct. If you do have the non-taper chainset or your BB axle is the wrong width for your new chainset, straight bottom bracket axles are out there if you search hard enough. I got one from Spanish
Ebay for mine which allowed me to fit a Stronglight Impact 50/36.
Alternatively, patience with a file will remove the bits of chainstays and seat tube which extend into the bottom bracket shell and allow you to fit a threadless cartridge bottom bracket.
Also, check if you have a steel or alloy front fork.