As you have discovered to find a factory moulded long DB25 cable is hard and expensive.
Stanwax has tha answer the "ILDA - CAT5 Adaptor"
Stanwax Laser ILDA to CAT 5 adaptors allow 1 ILDA signal to run from the laser projector to the control station using CAT 5 cables or CAT 5 infrastructure as long as it does not pass through a switch. It connects the most common signals using 2 CAT 5 cables and is sold as a matched pair.
To find long good quality cat5 cable is a cheaper and easier option.
here is a link to the product
http://www.laserknowhow.co.uk/product_p/ilda - cat5 adaptor.htm