The ticketing limitation is because of very strict currency restrictions that the Chávez government has instituted. Basically, individuals and companies are allowed to spend only a set amount of US$ each year (I think a few thousand USD per individual), and if they go beyond it, the government can sieze their assets and accounts.

What many of my friends do is use a credit or debit card issued by a bank OUTSIDE of Venezuela (usually in the USA, Canada, or Europe) to conduct all transactions in US Dollars. That way, they won't be limited by the Venezuelan restrictions, which in practice apply only to funds from Venezuelan sources.

So, I'm sure that a travel agent would be glad to sell you a ticket in Venezuela for an itinerary that does not include Venezuelan departing or arriving segments. But if you were to use a Venezuela-issued card to pay for the ticket, you might face some trouble. The easiest thing to do is to use a foreign-issued card, or ask somebody who has a foreign-issued card and then reimburse that person.