Hi Mary. Good question.

As to the need for a thesaurus in Esperanto: well, yes. The language has few exact synonyms, but a thesaurus is also useful for listing words with related, if not entirely synonymous, meanings. For that reason, I imagine that any language capable of conveying the range of subtleties in human thought will need one.

Offhand I can't point you to any standalone thesaurii. However, larger Esperanto dictionaries will include -- along with a word's definition -- a list of links to other words that are semantically related.

So, for example, if you look up bela ("beautiful") you'll find links to related words like plaĉa ("pleasing"), rava ("delightful"), sorĉa ("bewitching"), gracia ("graceful"), feineca ("fairylike"), pompa ("showy") and so on.