If you are buying from an industrial supplier they will be geared up to supply in bulk, by the standard length. The stores will be run by crane and forklift, and the delivery will be by big truck. All expensive to run. Anything else also needs extra time and effort, and who wants a standard length which has a bit missing so they cannot get their standard number of parts from it?
Just pop down to National Rail and ask them for six inches of railway line, delivered …
Tim