35w SOX is 12" end to end and almost 2" diameter.
55w SOX is 16" end to end, same diameter.
90w SOX is 20" end to end, 2ΒΌ" diameter.
The above will depend on the type of tube as some are more pointy at the end.
All SOX tubes have a U-shape inner arc tube within and a normal ''lightbulb'' ''BC'' fitting.
Ebay is the cheapest place usually. I'd look for SOX-PSG (they have a blue lamp fitting) as they're the newest kind and the problem of early lamp failure is almost eliminated with these lamps.
Sizes from 180w to 18w I think:
High Pressure Sodium lamps are significantly different and use screw-cap fittings only.