Two roaming vendors sell a pet for about 60 silver
Two vendors on the WoW Forever beta sell a pet for about 60 silver, but never stand still. Mayhoa Skyhoof walks through Orgrimmar, Lil Timmy through Stormwind. Each has one pet in stock, for one buyer at a time.
Mayhoa Skyhoof in Orgrimmar
Mayhoa Skyhoof sells the 
Prairie Wolf Pup Carrier, a new pet in Forever. It costs 63 silver and 15 copper on the beta. That price could still change before launch. The Prairie Wolf Pup has its own page in the pet guide.
Mayhoa belongs to Thunder Bluff, but she is listed in Orgrimmar. She does not wait at a stall and wanders through the city. Players have seen her in the Valley of Honor, past the pond near the fishing trainers, and between The Drag and the Valley of Wisdom.
She stops along the way and sometimes turns around or stands still in the middle of her route, players report. Where exactly she disappears, is not known.
Lil Timmy in Stormwind
For the Alliance, Lil Timmy sells the Cat Carrier (White Kitten) for 60 silver. He walks through Stormwind. Start at Cathedral Square and the canals nearby. Players have seen him cross the bridges and pass through the Trade District, Old Town and the Dwarven District.
He disappears near Cathedral Square and returns later. He has only one spawn point, so waiting at Cathedral Square works when he is not around. How long his respawn takes, is not known. The White Kitten is also in the pet guide.
How fast both vendors restock on the beta, is not known either. It may differ from earlier versions of WoW. Every other pet and where to get it is in the pet guide.
Source: Icy Veins