Rule of thumb from past business experiences , legit wholesalers generally do not advertise and you'd be hard pressed to even find a website sometimes. Most of them will require a business license, a state resale tax certificate, and a business credit line (they don't do credit cards) and with rare exceptions, they also require large orders (20 to 30 units? most wouldn't even listen to a buyer until they start talking in thousands of dollars at a minimum... maybe some of those chinese factories on Alibaba or some such might talk to you, if you want to go the import route, but then you got to deal with import/export stuff...) Most wholesalers will advertise in their trade publications (I.E. Textiles/Clothing/Outerwear markets, to connect with distributors and legit trade retailers) At best, you might be able to find an in-between (distributor) that can sell you smaller orders ($500 - $1000) but unlikely to get any custom logos, you'd likely have to go to a supply retailer for that.
Well read that post, and a search brings it up if you can figure out what SLSG is but it does bring up several links that may be suitable: https://www.bing.com/search?q=SLSG+smocks&form=ANNNB1&refig=2289436da6b14d959f1f5beb5b016b91