That is a little bit of an awkward situation! I usually try to wait until they look my way and then make a sign with my face or hand, but if it's taking too long I say "Prostite" or "izvinite" or address them as "Devushka" if it's a young woman and "Molodoj chelovek" if it's a young man, which feels slightly less polite, but both are widely used for addressing strangers and can work as well. "Mi gotovi zakazat' " would be another option meaning "We are ready to order".

AKI, I say простите) Извините is fully synonymous, both arе just 'еxcusе mе'. "Девyшка" and "молодой человек" arе usеd to addrеss pеoplе on thе strееt as wеll, not just waitеrs. I'm pointing at this bесausе - I'm not surе if you know this - in a numbеr of langugеs similar words havе bееn appliеd to waitеrs spесifically. Е.g. "человек" in 19th cеntury Russian, or "garçon" in Frеnch. Or comparе Еnglish dеvеlopmеnt with "maid". And no, no such thing with молодой человек and девyшка. Thеy arе univеrsal. But somе pеoplе indееd dislikе bеing addrеssеd this way, i can imaginе that waitеrs may likе thеm еvеn lеss. Thе problеm is that Russian doеsn't havе a Good way to addrеss pеoplе)))

I usually just say, "Извините", or if I have to repeat, "Извините, можно вас?.." (lit. "Sorry, can I have you?" but it's actually more along the lines of "can you spare me a moment?" or something like this). Some waiters don't like being addressed as "девушка" or "молодой человек" (though, as Margarita rightly says, it's not that uncommon to address them this way) so I think it makes sense to stick with the short polite options.

All the answers are valuable, and I cannot specify the best answer