Start at a local janitorial supply store---many of those also sell some type of office snack supplies, and may have some to sell you at a good price, or can help you find somewhere.
I think I have seen them in Dollar Tree but not sure. You might not be able to get the amount you need. I just searched online and found at bottomdollar.com and searched under plastic silver cutlery. They sell forks, knives, and spoons separately. Their boxes contain 20 per box and sell for $2.99 each. I also found a website yourparty.com and I think it was smartyparty.com. Both of them sold 600 per box for around $70.00. Good luck. Hope this helps.
I just had a thought, you might check online with Michael's. They sell all kind of party items too.
Login using the form on the top of the page to post feedback (if you are a registered user). If you have not yet registered, click here to do so. It's FREE!.