ribosomes are already distinguishable in unstained samples at TEM. You can find many nice pics of them in many books (https://books.google.it/books?id=ZozbQQAACAAJ&hl=it&source=gbs_book_other_versions).
You can label them with specific antibodies by pre or postembedding immunohistochemistry, but I would not recommend it unless you need to discriminate specific ribosome populations.
Immunogold labeling can be applied to be more specific, although in conventional staining by uranyl acetate and lead citrate, ribosomes can be nicely observed.
I don't need any particular stain or immuno stain to visualize ribosomes. Just follow the routine TEM protocol and routine stain UA and Pb acetate to stain sections. You will get your results.
in my research I'm trying to visualize mitoribosomes in a well preserved ultrastructure of the mitochondria which unfortunately is mostly compromised in immunogold labelling.