There are a few "bodges" to be done but best thing is to get NEW sprockets and chain ASAP. Also, keep in mind, your worn sprocket will have EATEN your chain and the front sprocket as well.

So, no point buying just a new rear sprocket, putting it onto a worn out chain and worn out front sprocket. Disaster in short order.

You need ALL NEW everything.
In future, you might consider keeping an eye on your sprockets and carrying some spares on board. One good tip is to change out your front sprocket about every 10,000 miles. I carry a spare front sprocket on all longer rides. Will extend chain life by about 20%.

The front sprocket is always the first to wear ... once worn will accelerate wear on both chain and rear sprocket. It's a system! and it's all quantifiable.

You may find a spare sprocket from a random bike of the correct pitch but the bolt holes won't line up. Try to RE-DRILL new holes in the sprocket to line up with those on your hubb. Can sometimes work.

Only other thing you can do ... and it's really a stupid thing ... is to tighten up chain (probably already done?) and oil the Hell out of it ... and ride on. Go easy, who knows, you might make it!

You could also have a machinist grind (by hand) out the sprocket, kind of reshape it so it will last a bit longer. Doesn't have to be perfect, just last enough until you can buy ALL NEW sprockets and chain.