Get a copy of MicroMart [out Thursdays]
for suppliers and advice.
Toshes are easy normally the HDD livers under the battery.
It does not have to be any particular make of drive- though other makes [IBM WD etc' screw holes may not line up, but this easily cured with double sided tape and the like.
The max siz of drive will have to investgated for the BIOS and operating system, other chums on this site will advise I am sure