I would first recommend emailing Rich at
www.richspsxparts.com this guy has everything and at great prices with free shipping most of the time. If its not listed on his page I'm sure he still has it available.
But if that doesn’t work try this.
http://tomekswholesale.zoovy.com/product/PS21AMPFUSE
The 1amp fuse is a little larger then what the PS1 fuse is rated at, if I remember right its rated at .4 amps. Also like I said before just cuz the pic looks like the larger ones doesn’t mean that what it is. I have seen what the 1 amp fuses from Tomeks page look like and they look nothing like the pic he shows. They are just a little larger the original PS1 fuse.