The FAR does not prohibit soliciting offers before funds are certified and available. However, FAR 32.703-2 and 32.706-1 require an availability of funds clause in solicitations in some cases to alert offerors that funds are not currently available. It is also wise to include a statement in the solicitation that funds are not currently available for the requirement but are expected to become available on or before (month/day/year). Your agency's FAR supplement may have more specific requirements for such cases.