It is not easy to source alginates and other gums locally so I tried to find some web based resources for those interested in spherification and other MolGas techniques.
I just used this search string “sodium alginate spherification supplies” in Google.
Try L’Epicerie – based in NY NY – the site is not so intuitive for all things, but their search function works well. On second thoughts, maybe it’s me that’s not intuitive. Go in to “Fine Foods” and the drop down menu has a “MolGas” link.
Bob’s Red Mill (Portland OR) sells guar and xanthan
WillPowder (Chef Will Goldfarb) also has an extensive range of products under these categories …
It is worth the read about Chef Will.
The Red Spoon Company sells ingredients and a starter pack (WillPowder does packages as well) -Woops, their first currency choice is Australian dollars – so I assume they are based in Australia – shipping might be a bit steep to the USA.
Chef Rubber is in Nevada – a bit closer – this is what they say about themselves… “Chef Rubber is a manufacturer and distributor of specialty items for World Pastry Champions, Artisan Chefs and Confectioners. Our extensive selection of products makes Chef Rubber a viable resource for the creative and innovative.”
Le-sanctuaire looks interesting too; also source of the English language version of Apicius: Journal of Haute Cuisine a semi annual publication – but even with a three year subscription it’s $47USD an edition.
I am not endorsing these sites – but they seem on the up and up – personally I would be happy buy from them, at least one time to try them out and then decide – I have purchased online from Bob’s Red Mill numerous times with no problems.
You can also read about Erik Foodladi/Fooducation’s first spherification experience here http://www.fooducation.org/2009/02/my-first-spherification.html
Late edit – look at the comments – Martin Lersch from Khymos has a more extensive list of suppliers and he has posted his link in his comment.