Square-D/Telemecanique (Which is handled by Graybar)and Namco
These 2 groups where the majority of what I used in the past. If you tell them what kind of environment...they can help you determine what level of protection that you need.
I think it is better to classify the hazardous level of that particular area first, e.g. zone 2 area, zone 1 or even zone 0. For zone 0, the most dangerous one, what u can use is Ex'd' or Ex'i' type equipment, zone 1 with Ex'e' and zone 2 with Ex'n' etc. Wrong area classification may incur high cost in Ex-equipment selection.
If you want to specify an explosion proof switch then as per IEC you can specify Exd or Exde.
You can aslo add the gas groop environment ie IIA/B/C and the temp rating say T3 and finally the ingress protection (IP) rating of say IP56 for general outdoor application.So adding everything together the total spec for the switch would read
Exd,IIB,T3,IP56 or Exde,IIB,T3,IP56
Note that an Exd switch will cost more as it will have a metal housing but will be more rugged too, while Exde will be relatively cheaper as it will have a plastic (GRP) housing but not usually specified for rugged duty.
Finally, it is not permissible (by IEC) to use or specify Exd or Exde devices in zone 0 where only Exs ( s being - special design) would be permitted for power application devices.