Variants of the Enigma machine had been sold on the commercial market from 1923. These could be bought by other countries - both the Spanish and Italians used unmodified Commercial Enigma machines, while the Swiss , Bulgarians and Swedes each had their own special version. The British Typex machine was ultimately descended from a Commercial Enigma machine. Meanwhile, the Dutch and Hungarians bought the H29 military variant of the Enigma machine. The Japanese were shipped a special variant from 1943. However, all of these purchases occurred before the period you're discussing. In the post-war period, users of Enigma can be divided into three main groups - those that were using Enigma pre-war, those that had been occupied by the Germans, and those that bought Enigma as a cheap option. The first group encompasses the nations mentioned above. The second group mainly consisted of Norway and Austria, both of whom had large supplies of Enigma machines easily available. The final group are mainly post-colonial nations, such as India, Pakistan, Ghana and Nigeria.

Why would these nations buy Enigma? Firstly, these machines were available for much less than competing machines of a similar level of security. The main producer of these was Boris Hagelin's Cryptoteknik, working out of Switzerland. This company produced several types of machine similar to the Enigma, but costing just as much, if not more. The Hagelin machines were, at least in theory, much less secure than Enigma - they produced a smaller mathematical keyspace, making them easier to crack. Secondly, the fact that the Allies had cracked Enigma was a secret well into the 1970s. The British government maintained secrecy about the effort at Bletchley Park and elsewhere until the publication of a popular history book, F. W. Winterbotham's The Ultra Secret in 1974. This secrecy meant that while buyers had their suspicions, they had no proof that the British could read their messages. Finally, many of the buyers were much less worried about the British reading their messages. Many of the buyers had strong regional rivals, who were their main priorities. While Britain could afford to spend money to break and read Enigma messages, very few of these developing nations could afford to. As such, buying a cheap cipher machine that the British might be able to read but your neighbours certainly couldn't was a strong proposition.

The enigma codes had to be cracked anew for each day. To do this required a huge volume of signal traffic; they had to intercept that, and then keep looking through it all, trying to find one operator who made a stupid error that would reveal the rotor settings for that day. Even knowing this, that would only let you decrypt a single day's message traffic. It all had to start over the next day. All of this required a huge amount of resources, either dozens and dozens of decoders trying to find that day's key, or hours and hours of the "bombe" computer time (along with it's technicians).

For low volume traffic, the enigma was probably unbreakable. Even if you could break it in theory, the resources needed would have been an incredible expense. All this measured against countries (or companies) that often didn't have a huge strategic importance.