Keil has an evaluation version of their C compiler at www.keil.com that includes an excellent assembler.

If you purchase an evaluation board from Cygnal for one of their processors (see www.cygnal.com) you also get a "trimmed" set of the Keil tools similar to the evaluation version I mentioned first except that the assembler and linker are totally capable and can make programs of the size you desire. In the Cygnal version only the C compiler is crippled. The Cygnal evaluation kit, with this software, costs 99 US $ and is quite a good deal and a nice way to get a full fledged assembler.

Hope this helps by giving you another alternative.
Michael Karas