Small piece of roof felt

[Sue]

I need a piece of roof felt for my small lean-to shed, to fit 120 x 50 cms plus whatever overhang is needed on the four sides.

Somebody in my road kindly gave me a roll last year, but it disappeared from the front of my house (I didn't have the use of my garden at the time).

If anybody can help I would be very grateful, as the roof is presently leaking at one end 😭