Getting sample products to promote on your review site?

If it comes to selling digital products then you will have a high success rate. I once went on clickbank and requested a sample copy for 5 products I wanted to promote - and 4 timed they immediately handed out a review copy.
But I think, however, it will be difficult for physical products since they also have a manufacturing value.
Just make sure to point out what's in for them and maybe show him some previous work. Because in the end, you still provide the income for him.

Kindest regards!

Create an email that can be quickly edited for the specific product in mind and start sending them to the manufacturers that you want to review.

It can't hurt and this has worked in the past - I've done it myself albeit on a much smaller scale.

Send them the link to your site and see what happens.

In my experience it makes a huge difference if you're established. Examples:

I had a palm pilot site many years ago, and I regularly received cases, stylus and other accessories to review. Plus tons of software. The site had 300,000 visitors a month though, and I worked on it extensively.

I did the same with a gadget site similar to Gizmodo and also easily received review items even though the traffic was probably one-third.

Then I did it with a book review site. That one only had a few thousand visitors each month but I wrote extensive, honest reviews. Again: I put a lot in to it. I quickly found myself with a huge backlog of physical books to review. To this day -probably 10 years later - I still get review inquiries because of previous work people stumble across online. And no, I don't have the site anymore

In all cases I started by reviewing what I already owned. Some people simply buy products, then return them after the review.

A critical point for success: create outstanding, detailed, honest reviews. The better the quality, the faster you'll get noticed by the PR people who send out sample products.