Is please advise if you are available for a conference correct grammar?

The grammar is technically correct, but it sounds a bit awkward and informal. Here are some better ways to phrase it:

More formal:

* "Please let me know if you are available for the conference."

* "Would you be available to attend the conference?"

More informal:

* "Are you available for the conference?"

More specific:

* "Please let me know if you can attend the conference on [Date]."

* "Would you be able to attend the conference on [Date]?"

The best option depends on the context and your relationship with the recipient.