co-worker ardent in selling me chess pieces

Not how it goes.

You may be a wiene!

This is known as a 'First World' problem...

" As soon as I have the money or the opportunity I will let you know, I appreciate the offer "

Why is this even a problem? Decide what you'd prefer:

a) You don't say no, and so you spend money

b) You say no, and save your money

Which of those options most appeals to you? If the desire not to say no is greater than saving money, go ahead and buy them. If you'd rather not buy them, say no. This isn't difficult, just make a decision and stick with it.

Just buy the chess pieces man.

The medical costs involved in having pair of balls grafted onto you is far higher.

Duck's dependable diagnosis

If you don't want to say no, then buy it.

Actually, never mind. Forgot he was your friend. You should just say that you don't need a chess board but he should sell it to (insert name here).