There are kits for printing decals on an inkjet printer but they
usually use a clear plastic substrate like Mylar with an adhesive
backing.  This leaves a thick, clear surround for your decal.
Suppliers of model decorating materials have a similar product with
thinner plastic.

But there are several small companies that make decals to order on what
appears to be a varnish backing.  They use a film ribbon on an impact
printer (like the Alps dot matrix printer that does 2400 dpi) and the
results are very good.  They can even do shiny metallic gold and
silver.  Another use is to decorate fire trucks (or pickup trucks with
calliopes in them).

If anyone is interested, let me know and I'll dig out the contacts for
them.

Craig Smith