I bought a vintage Sencore P57 that was "restored" and "calibrated"

It requires a fuse I can't seem to find.
105/125 VAC 60Hz 625 Watts
FUSE: 3AG 4 AMP Slow Blow

The current one it came with is 250v. I did find some but only in 5mm x 20mm unfortunately, I bought them before thinking about size. It needs to be 6mm x 30mm.
I want to make sure I have the correct fuse before I start using it.