The question you have asked is very generic and you should Expect changes in the answer as you clarify more details about what workflow around the accessing this information. but my first take based on what so far you have given is as follows:
Information about the Book is rarely changing or less frequently changing information depending on what attributes you have included here. On the Other hand "Availability" is probably very frequently changing attribute. Lets say you Define "Availability" with as simple indicator Yes/No as possible values.
putting this column on the same Table will have PLUS point is your read query will involve only one table but down side is as the "Availability" changes the update is going to be the against this large table. different type of read query can be requested against that table and down the road you might find Availability is not that important for 60% of the query user is doing on this table; and hence that will affect decision what column are part of Indexes. this table might need "FULL-TEXT", "FILTERED Index", "Fuzzy Search" etc....
Putting this column on a new table has a plus point that 90% of time update query against this table will involve "BookID" and "Availability" column in them so you can optimize the indexes on this table as you like w/o worrying about the performance of Read queries on the other table where mostly constant information of Book is stored.
now as you can see above is applicable IF the possible values are "Yes/No" or "0/1" etc.... as your definition and Implementation of "Availability" changes, you have to re-evaluate your decision.