Does anyone know where I can buy large quantities of pecan nuts, walnuts
and pistachios i Pattaya? I've only been able to find 100/200 grams
bags at Makro.

I always buy large quantities on the motorway stalls, which seem the best value for money. However i always buy cashew nuts which they have, but i have not seen pecan, walnuts or pista....o's although i have not really looked for them.

If you have not looked already try there.

Sorry I saw you said in Pattaya, so ignore my comment, although there are some of those stores pretty close by.

There is a nut stall at the market near the beach in Nakua (the one with fish), hard to explain exactly where as it is a bit of a labyrinth. They also sell lollies (candy) and dried fruit, you can buy prepacked 400g (aprox) packs of ask them to bag up what you want. Go for for an exploration trip you might find lots of other things you did not know you needed.

The bakery store on Sukhumvit is a great source of nuts (and raisins and flour and other bakery stuffs). They have cashews, almonds, sometimes pecans.

If you travel south on Sukhumvit from Naklua and pass the traffic lights on the road to the weekend market (Sawangla Road?) it will be on your left a few hundred meters down, past a second set of lights, on a corner (Sukhumvit Pattaya 31 Road?). If you see the big Home Pro type store, you've gone a bit too far--park and walk back. It's easy to miss, but a good resource when you finally find it.

http://goo.gl/maps/SzxzM

This one surprised me. I never thought that anybody would have trouble locating nuts in Pattaya! ... (Sorry, I just couldn't resist.) :-)

There's a small shop near TukCom. They sell various things like nuts, dried fruits, and even dried seafood.

From TukCom main entrance, walk West (towards the sea) about 2 sois, you will see the shop on the left.

This is not going to help you one bit ,but we all know how much pistachios cost for a small bag here in Pattaya ,but my sister has to go to a market near the border once a month and she gets me a 1/2 kilo bag for 190 baht ,yet here they cost an arm and a leg ,amazing thailand

This one surprised me. I never thought that anybody would have trouble locating nuts in Pattaya! ... (Sorry, I just couldn't resist.) :-)

Was going to suggest you try Hospitals that specialise in the operations taken by “Lady boys”

But I won’t

Some replies are for finding half kilo packs. I suppose large quantities in bulk would mean a few tons at least?