Try a boot sale or computer fair. You could try visiting your loacl independent computer store (I men NOT PC World, Maplins etc. these stores are great for other things) and get chatting to some geeks (oops, I mean computer enthusiasts) who might lend you one. Of course, no one would possibly consider copying the disc for you as that would be illegal and a breach of copyright (haha), and of course you have a licence to use the programme.
Although if you're referring to the 3.5 inch floppy disk that is used to boot the computer prior to the installation, rather than the Windows 98 CD itself, you can download images of the floppy from the internet, and make yourself a new one.
WOW.. someone still uses Windows 98.
I have used win95, win98, win98se, windows ME and now use windows XP pro.
Windows98se is far better than winm98.
I have both CD's laying around somewhere.