Objectively, how many 6'7" dive customers do you think are in Thailand? I think you'll have problems in 2-3 areas.
Are you just tall or also big? If you're tall but thin it's better than if you're heavy since that brings BC sizing into play.
Fins might be one issue if you have proportionally sized feet. Many shops only rent full-foot fins and may not have them in your size. If you're pretty sure you plan to do this you might buy boots and
open-heel fins locally to get the proper size/fit. It's likely you'll have to buy/provide fins/mask/snorkel for your class anyway so invest in good gear. If you do buy a mask, do that locally since
fit is the only concern. A $15-20 snorkel will be fine for class (required) and may be the last time you need one.
Most wetsuit sizing stops at 6'5" or less. I'm not sure if you can get 2" of stretch out of one.
Maybe if it's lightweight (2-3MM) it might. Of course if a shorty wetsuit is all you need in Thailand (that's a possibility) you might be OK with a rental. Or buy one here first, they're under $100. Lots of choices here:
Buy scuba gear, scuba diving and everything underwater from LeisurePro.com if you don't have a local shop nearby. They offer their PFF (Personal Fit...) guarantee so you can return something undamaged if it's too small.
Even if the water is warm, you want some exposure protection since doing multiple dives will lower your core temperature. And you'll be spending a lot of time in class in the water doing skills and waiting around for everyone else to finish. Also there are a lot of sharp (coral) and stingy (jellyfish, fire coral, urchins) things you might accidentally brush up against so some protection is good to have.
One thing you might do is try to find the tallest 1MM full suit you can buy and see if it will stretch enough. I have one sized for 6'2" and I'm 6'4" and it's tight but works. Another option is a Lycra dive skin - they aren't typically sized as large but if you could find a tall one it would help. Lycra is a lot stretchier than neoprene.
Look under skins and wetsuits on the LP website for options. Or check Scubatoys.com, DiversDirect.com, Diverssupply.com, diverightinscuba.com or scuba.com.
For a BC, typical rentals are jacket models. With velcro and adjustments, many are a pretty universal fit. In your case your tank (and weight) might be a little higher from your center of gravity than standard but as a new diver, you'll hardly notice. If they have some larger BC rentals, less of a problem also. I use an XL at my height and I have a long trunk and short legs. Stock sizes go to 3XL from several common mfr's who supply rental gear. With a jacket rental, you'll probably rent a weightbelt also so that weight will be in the correct location.
Later when you're diving, you might look into a Backplate/Wing BC. They're modular so components can be sized to fit. One vendor - DSS - sells a "long pattern" backplate that is probably one of your better options.
https://www.deepseasupply.com/
If you don't do any of this, I'd communicate your size needs up-front to the shop you plan to certify thru - if you have one selected. If not there are resources here in the Thailand Forum to help with that.
You might sign up and do the e-learning before you go, that allows you to only have to do the skills training and certification dives when in Thailand. Check with the shop on that also as sometimes they provide an e-learning code that links your results to them.
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