Austria Adapters / Converters

Try starting here: https://www.ricksteves.com/travel-tips/phones-tech/electric-adapters-converters
I expect the same will work in both countries, but we have no experience in Greece.

Are you sure you need a converter? Most modern electronics are dual voltage. If is says 120-240 all you need is an adapter. The same adapter for both countries.

Rick Steves sells them or do a search on Amazon.

What kind of electrical equipment are you planning on plugging in?

According to this website, both Austria and Greece use the German Schuko plug (Type F) with side grounding clips and the two pin Europlug (Type C). Note that the Europlug is limited by electrical codes to applications of less than 2½ amps (575W on 230V), so it would not be acceptable for a hair dryer.

Also note that devices with polarized plugs (one blade wider) should not be used on the European continent.

I'd suggest being "cautious" with Voltage Converters, as they can cause problems. There are two different principles used in voltage conversion, and using the wrong type can damage equipment.

It would help if you could indicate what devices you'll be travelling with? It would also help to know whether any of your devices have grounded (3 pin) plugs. As mentioned earlier, the devices you'll be taking may be designed for operation from 100-240 VAC, so in that case you'd just need Plug Adaptors. I'd suggest taking at least two Plug Adaptors, as they're small and easily misplaced.

If you don't feel like mailing away for them, Staples sells multitype adapters in-store, other local stores may, too.

ACE Hardware sells adapters.