How do I source prizes and gifts for a competition site?

Every day I receive invitations to win holidays, gift vouchers, cash, cars etc. When you go to the site there are literally hundreds if these deals listed.

I know some of these sites simply compile a list of the competitions they find but some of the sites are generating their own competitions.

How would I go about getting companies to sponsor gifts and prizes for my own site?

I know people will say I need to speak to the companies that are running competitions and get them to sponsor something on my site....but how long would this take. Some of these sites literally have hundreds of comps on a daily basis....and as they are all free to enter where is the revenue to drive a procurement team?

It feels as though I am missing a trick........though probably not.

The site is built-in ready to go. the development team are ironing out a couple of final bugs.
I believe I have a unique product here. Maybe people on the forum will think differently.
There are reasons I did not source the sponsors first...
A. I wanted to build the platform first so I would have something concrete to show potential sponsors
B. This company sponsored category is only one part of the functionality of the site.....in fact I am only using this aspect to drive traffic to the site. I am offering cash prizes out of my own pocket at this moment. But this is not sustainable in the long term.
C. I wanted to build a database of people on the site to give me some bargaining power.

Last thing...each company which sponsors a prize will be able to collect basic marketing information from each person who enters.

I eagerly anticipate your responses.

If you're selling affiliated products, the affiliates dish out prizes to the top affiliates each month - you are then free to either keep these or pass them on as prizes to your users.

Alternatively, if you have great traffic and a reason why a company would gift you something to give as a prize, then go that way - typically this happens when a company is promoting something new about their company. The companies wish to give prizes out as a marketing ploy - to generate awareness and enthusiasm for their product - but they're not going to give you prizes if you only have 1000 visitors per day, for example (unless you're HIGHLY niche).