Brands
The majors brands in alphabetical order are
Which brand you go for is a matter of personal preference and it’s a good idea to hold the chisel in your hand before purchase. The Kirchen tools all have an octagonal handles which you’ll either love or hate. The Pfeil tools often get praised on-line for their over all balance and quality.
There is also a wide selection of cheaper brands available but the quality can be variable at best. While you can get away with a cheap straight chisel a cheap carving gouge is likely to be more frustration than it’s worth.
Tools Measurement
If you have an unknown gouge in your hand and you want to measure it it’s tempting to get out the callipers and and measure the outside diameter of the tool but this will give the wrong result. For the more deeply curved and smaller diameter tools the result will be a long way from correct. What you should measure is the flute and in particular across the flute at the tip of the tool. This image will hopefully make it clearer:
The easiest way to make this measurement is to stab the tool into a piece of scrap wood and measure the corner to corner distance with the points of a pair of calipers. Trying to measure the tool itself is an exercise in frustration.