I would like to sell Dr. Sear's book (The Baby Book) on my website. Is
it possible to buy only this title wholesale and if so, how do I go
about doing it?

Contact the publishers.

If they won't sell to you direct, they may recommend a wholesaler.

The easiest way would be to sign up as an affiliate with eg Amazon.
Although the commission is modest (about 5%-10% compared to the 30-55%
of being a traditional bookseller) they handle all the card billing
and shipping for you, which may be useful if you do not already have
ecommerce and warehousing/fulfilment facilities.

Owain