I know that Milan researchers interested to work in modern and efficient isotope laboratories go to a place near to Croatia....to Trieste science park - http://www.area.trieste.it/opencms/opencms/area/en/.
I wouldn't hesitate to recommend the Scottish Universities Environmental Research Centre in Glasgow. They have a variety of different methods to run O isotopes. Contact Prof. Adrian Boyce, I'm sure he'll be happy to help or discuss your needs
But are you sure? I think here: INFN - National Institute of Nuclear Physics - Trieste Section, or in PicoSaTs S.r.l. sector: Physics, materials and nanotechnology, Trieste Science Park
I recommend you to contact Heather Stoll at University of Oviedo (Spain). As far as I know, she is one of the pioneers in geochemistry with coccoliths and diatoms and her lab is a good choice.
I worked with Professor Joachimski (http://www.gzn.uni-erlangen.de/en/lithosphere-dynamics/staff/faculty/joachimski/) from the Erlangen Nurnberg University (http://www.gzn.uni-erlangen.de/en/lithosphere-dynamics/ausstattung/isotopenlabor/). He analysed carbonate terrestrial sediments for me. I would highly recommend him without any doubt.
Ján Veizer Stable Isotope Laboratory (formerly G.G. Hatch) is one of the best labs with variety of different methods and equipment. They have AMS, LGR, EA//IRMS, TIC-TOC, Gas Bench deltaXPlus, LSC......
You can contact with Paul, Monika, and other very good technicians.