For 1999 (And really anything beyond around 2008 at this point), most of these have long since been discontinued from Mitsubishi.
Your best bet for finding an owners manual or service manual is going to be looking on ebay for a used one.
The only one I see currently that would be a good match for the owners manual is this one:http://www.ebay.co.uk/itm/MITSUBISHI-SHOGUN-PAJERO-OWNERS-MANUAL-OWNERS-GUIDE-HANDBOOK-MIT-135-/151751991282
For the service manual things are even harder... because the service manual sets would run well over $300US it is rare to find anyone that bought them, let alone bought them and then wanted to sell them at an obvious loss. The best way to get your hands on a genuine manual set is to find a Mitsubishi dealership that went out of business recently OR one that changed to a different franchise that no longer services Mitsubishi, but still has the manuals around assuming they were Mitsubishi long enough ago to have this old of one around. Not a very easy scenario to come by either way.
Because of that most people will opt for a third party manual like a Haynes etc. These are FAR from ideal, but they will get you most of the information you need, they are just lacking primarily in wiring diagrams (and accuracy of the ones they have), and year to year minor changes.
There are however a good deal of people that sell gray market CD copies of the original manuals (As well as CD copies of third party manuals). These can often be had for very little money, but apart from the legalities of it are usually suitable. The way to tell the difference between a third party copy and a factory copy of the manual is that factory copies will rarely be more than 1-3 years total in a manual. Third party manuals are very often covering 4-5 or even 9 years etc... factory manuals never cover that broad of a span due to all the changes from year to year.
I know this is not ideal, and I do wish I could just give you a part number to order from your dealer for real cheap, but unfortunately it just isn't the case when we start talking about 15-20+ year old models... the support just isn't there any longer and your options are very few.