Hi @Dhruthi,
Welcome to the QIIME 2 Forum!
We do train and provide Silva classifiers, but not UNITE classifiers at this time. You can access these from the QIIME 2 Resources page. Note that sometimes the Galaxy servers lag behind the most recent QIIME 2 releases, so just be sure to use classifiers that are written for the version of QIIME 2 that the server is running.
You can find some information on training your own UNITE classifiers here. I haven't done that on Galaxy before, but I think it should be possible.
Greg