I discovered by accident (I was looking for something else) that on the following webpage

http://technet.microsoft.com/en-us/security/dn481339

if you go about halfway down the page you come to

Search by Product or Component

and from the Product/Component dropdown list you can select Win 95 or 98 or 98se or even 3.1 and many Windows and other Microsoft Updates can be obtained going back to the mid 1990's.

Apologies if this is already well known to everybody except me!

Microsoft too often buries that kind of useful page. This link is a list of Knowledge Base articles sorted by product, which is something similar: http://kbupdate.info/