I intend to move to Bangkok and look for an apartment after I get there. I want to post a parcel to pick up after I arrive but I do not have an address to post it to. I estimate it might take a couple of months for the parcel to get there. Does anybody have any idea how I could go about this?

Have a friend hold the parcel until you have an address in Thailand and then have your friend send the parcel...

It is quite a large parcel. Is there a commercial service I could use?

Enquire with Thaipost. I believe they have a service where you can address it to yourself and the Post office address in that area and mark it "for collection".

Address it to Poste Restante at whatever Thai Post Office will be most convenient for you.  (That is "General Delivery" in French, and is the internationally understood term.)

I can't say how long they will hold it for you; I think it is 30 days.  Check with Thai Post online if you can.

Check the nearent post office to your address and address parcel to post restante at that post office. Keep postal receipt for collection. Small charge of a few baht on collection. 

I have used this service many times works well