Is this for the old 5400, or the 5400z? If the old model, it's not hard to do yourself if you can't find anyone- all you need is a null modem cable (nine pin, female at both ends), and the WDN4OAK software that you can download from the Humax site at
http://www.humaxdigital.com/CS/Default.asp
The patches can be found in various places, such as
http://www.axs-ict.nl/humax5400/
(if you do do it yourself, make sure to wait until the patch is fully loaded onto the machine before turning off- there is a delay between the computer display showing completed and the Humax showing "end")