I am not going to tell you to break the law, it would be best to fax/email the Thai Embassy where you live and ask them , and keep a copy with you,

Saying that , I doubt that anyone displaying or going to a trade show at Bitec ever got one , unless that was the only way to get into Thailand if they could not get a visa on arrival like most of us can.

But rules are made to be broken, and in Thailand enforced when they feel like it
so some people in suits and briefcases have been stopped and ask for their work papers, around Sukhumvit tourist area, but thats not likely, and was more a shakedown for a small "gift" from the nice policeman.....

I would not worry about it unless you are bringing so many samples that you need help getting them thru customs !

Have fun

Rally