Below is a short list of stable isotope suppliers, mainly labelled compounds. Information for standards can be found here, with lists of analytical labs here (commercial) and here (academic).

Stable Isotope Suppliers

Sercon Limited

Sercon are the UK distributor for the complete range of stable isotope labelled compounds

Cambridge Isotope Labs
Spectra Gases (18O water-see CIL above)
ICON Isotopes
C/D/N Isotopes
Omicron Biochemicals (sugars, nucleosides)
Sigma Breath Test
Los Alamos National Labs, stable isotope resource
Goss Scientific Instruments Ltd (UK)

Consumables Suppliers

Sercon Limited

Sercon supply consumables of the highest quality for all isotope ratio monitoring mass spectrometers and elemental analysers. Our unique approach of providing the highest possible quality at the most competitive prices means that now all users can benefit from our products.

Isomass Scientific (Canadian supplier)

OEA Labs Ltd.

OEA Labs manufacture and supply advanced products for organic elemental analysis (OEA) and elemental analysis isotope ratio mass spectrometry (EA-IRMS).