After many years of being involved in the sea glass community, you soon get a feel for where the 'best' sea glass comes from. Best is subjective of course but I would classify the best sea glass as being the rarest colours and the most perfect flawless pieces. They would be graded as jewellery quality that can be used for sea glass jewellery.
Particular countries that stand out are the UK (Seaham seems to be the place to go), Spain, Greece, Japan, USA and Puerto Rico. Quite honestly though, most countries that have a coastline have something to offer in the way of sea glass.
I have seen some amazing pieces being found in Australia, Italy and France. Also some seriously impressive nuggets coming from such farflung places as the ABC islands (Aruba, Bonaire and Curaçao) and St Kitts.
Here in Cyprus, there is indeed sea glass. It has taken me years to discover a few good beaches that give up the goods, so excuse me if I don't give my locations away - it's a trade secret! I don't particularly find the really rare colours here like red, orange or yellow but I do find good amounts of white, greens, sea foam and browns. Occasionally I also find the elusive blue and some turqouise sea glass and have also found some other colours of interest such as lilac / lavender colours.
If you're lucky enough to get the opportunity to go to the beach, have a look around and see what you can find. Maybe you will uncover some sea jewels and get hooked on the hobby?