I think sponsored reviews the way you suggesting to do them, getting a review by sending samples, is a good idea and is alright. Guest posting also should be possible on different food related blogs, some quick examples of blogs I found from a search in Google [they may not be directly relevant to your line of business but I believe you still can write something for them and get a reasonably relevant link in return]:
http://www.farmtotableonline.org/write-for-us/
http://www.eatwithme.com/about-us/
http://eatdrinkbetter.com/write-for-us/
Apart from that, I believe you should also have a blog section on your site and create interesting "link worthy" content that when properly promoted could draw you a few good links. Link building is not only about "building" links but also about "attracting" enough links. So you have to work on that as well.
I personally believe submitting to directories whether they're the free general directories, the paid directories or relevant food industry specific directories, they all would offer you some amount of value in the link that you get from them. Just make sure you don't target a single term when building links with the directories, you want to target a large set of seemingly "natural" terms so that you don't suffer from any possible "over-optimization" penalty in having too many links with one or two anchor text.
