I've got a 1251 I got off the 'bay a few years ago. It came with a sanding disc, a sanding drum, a dado set and a router bracket.
I've found that if you keep an eye on the 'bay that various standard attachments are offered from time to time.
The only extra that I have bought is a pair of adjustable angled fences for the table - Miles Tools put these on the 'bay and I got them for about a third of the normal price - they were brand new still sealed in the DW box.
As for router brackets there seem to be two different versions - I've got the small one that will accept the small Bosch 500 type router (88mm motor housing) but there is a larger version that will take a number of bigger routers. The thing is that having the facility to have an overhead router ought to be useful but so far I've not actually tried - I'm used to using routers handheld or in my homemade router table.
Both the sanding disk (about 10 inch diameter) and the sanding drum (about 2 or 3 inch diameter) really need to have auxillary tables made for them.
The other thing about most of the attachments is that you have to do a lot of fiddling around to remove and attch components which can be a bit of a PITA - the only attachment I tend to use (ir)regularly is the dado set.
You occasionally see moulding sets available but I woulf not be comfortable using these. I've seen Norm on NYW using these on his table saw and thought that I wouldn't want to be in the vicinity when they were in use.
My saw came with two manuals - the adjustment and operating instructions covering 1251, 1501 and 1503 - a total of 26 pages. Also included was the Dewalt Powershop Handbook on how to make the most of your radial arm saw. This is 130 pages and actually refers to the 320 and 125 models. It covers basic cuts, the dado head, the shaping head, the disc and drum attachments, the router attachment, the sabre saw attachment and the drilling attachment. It also includes a chapter on the adjustment of the machine.
If you get no joy with obtaining manuals then PM me and I'll scan the documents and put them into PDF files
Misterfish