Is there any source online or catalog that features 5-40 nuts, screws, and other items such washers, etc. that could be used for slot car applications?
There is two places that I know of at the moment that features tons of screws, nuts, bolts, washers, etc. One site is www.microfasteners.com which has a good assortment at decent prices and www.smallparts.com which carries the same parts with many more items. The Small Parts Inc. catalog has over 400 pages filled with various tools and parts with some items relating to slot car applications. I highly recommend getting a catalog from each of them.