Thai work permit cancelled, can I get a tourist visa before leaving?
You can not apply for a Tourist Visa inside Thailand, it has to be done at an Embassy or Consulate. You can only extend a Tourist Visa within Thailand and that can only be done once for a cost that is about the same as applying for a new tourist visa.
I don’t think your employer can cancel your ‘visa’. They can get your work permit cancelled, but in terms of your visa at best they can withdraw their intent to hire you and thus keep you from renewing your visa.
Depending on your citizenship, you can leave the country and perhaps come back in under the Visa Exemption program for 30 day stays. But coupled with you recently expired visa for working, it may generate suspicion of trying to live in Thailand without the correct visa if you do this a couple of times in a row. The government has been cracking down on expats who used the 30 days Visa Exemption to live in the country.
You can also visit a Thai Embassy in neighbouring countries to apply for a tourist visa, which if you get one of the newer multiple entry ones gets you several 60 days entries. But again your expired visa for working may be taken into consideration, as proof you intend to reside not just visit.