It has just been announced that Poland will hand over it’s Mig jets to the USA for handing on to Ukraine.
Now this could start a trend for NATO and give Putin heart failure. I bloody hope so!

Within NATO, only Poland, Bulgaria, Slovakia and the US operate Mig-29s.
Poland also operate about 50 US made F-16's, and these could probably cover for the 'gifted' 20 odd Mig-29s whilst replacement aircraft are supplied to Poland. Poland has 24 F-35's on order, plus options on another 24, but the first of these won't be delivered till 2025.
Slovakia and Bulgaria have no other options though. They have ordered brand new F-16's, but these aren't due for delivery till 2025-27 and I don't think they have any pilots in training yet. Even though they both own more than 20 Mig-29's only a handful have actually flown in the past 5 years. It's doubtful either country could get more than 8 airworthy on any one day.
The US 'obtained' an unknown number (around 12) of Mig-29s from Moldova when the Warsaw Pact disintegrated. These were used in 'special programs' at Area51 and Tonapah. Most are now preserved or in museums, but a few are believed to still be "active".
The only other current operator in Europe is Serbia who have 14 recently upgraded Mig-29's. However, they're generally fairly pro-Russia, so I doubt they'll want to get involved.
Past European operators include Hungary and Romania, but their aircraft haven't flown for probably 10 years, and are currently just littering their ex bases at Constanta and Kescekmet. Moldova still have 6, but they haven't flown for 30 years. Can't see any of these being any use quickly. The Czechs and Germans did operate them, but sold them to Poland - that's where most of Polands 30 aircraft came from in the first place.