Unless you are a high-end customer of a high-end and well-established TA, it is highly unlikely that you will be able to obtain a ticket without full payment and hard to have a reservation held for an appreciable period of time.
If the reason you are asking this question is that you must show proof of a ticket, then a fare lock will not suffice.
You should check the COC for the various carriers you are considering. Some will consider the denial of a visa a sufficient reason for a refund.