As discussed in Components, other than GPC itself, you need an assembler, linker and friends, a C library and possibly a debugger. The site http://www.delorie.com/djgpp/ recommended the following files and they will help you find a mirror:
v2/djdev203.zip | (C library)
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v2gnu/bnu2951b.zip | (assembler, ...)
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v2gnu/gcc2952b.zip | (gcc)
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v2gnu/gdb418b.zip | (debugger)
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v2gnu/mak379b.zip | (make)
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v2gnu/txi40b.zip | (texi)
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This list is about 10 MB not counting GPC. You can use a binary version of GPC from the web site.