There is **no set amount of chains that will guarantee** that you will encounter a Pokemon with six perfect IVs; your chance of finding a Ditto with six perfect IVs is therefore left down to probability. Unfortunately, that probability is not in your favour at all. With the chaining method, you're going to run into a lot of 4 IV Ditto like the one you have, a few 5 IV Ditto and almost none with 6 IV. If you're after a 6 IV Ditto only, chaining is not worth your time.

The highest amount of perfect IVs you can *guarantee* with the chaining method is four, which is achieved with the 30th chain. After that, any further perfect IVs (ie. a fifth or sixth) are based on pure luck. Your chances of finding these is fairly simple probability: for 6 IVs it's simply (1/32)^2 which is **1/1024**, abysmally low for something you can only attempt each time a 30th Pokemon is chained.

If you'll settle for a 5 IV Ditto -- which is usable but will take a bit longer whilst breeding -- your chances of finding one are **63/1024**, or about a sixteenth. (That's the chance of one IV being perfect added with the chance of the first one *not* being perfect and the second being perfect, or 1/32 + 31/32 * 1/32.)

The sad reality is that **there is no easy way to get a 6 IV Ditto**. If you'll accept a 5 or 6 IV Ditto whilst chaining, you can have 6.25% chance of getting one each time you chain to 30 Ditto -- otherwise, you'll have to look elsewhere. Pokemon sub-Reddits, especially /r/BreedingDittos, /r/pokemongiveaway and /r/PokemonTrades, are the best places to look in my opinion as they have the largest group of people all looking specifically to make trade deals.

Basically, it's **possible but highly improbable** that you will find a 6 IV Ditto using the chaining method.