Display stimuli randomly based on previous stimuli in qualtrics

I use qualtrics for displaying stimuli to participants. I categorized my stimuli on two dimensions.

The first dimension is represented by a letter (a,b,c)

The second dimension is represented by a number (1,2,3)

So each stimulus can be one of the nine combinations letters * number (e.g., a1, a2, a3, b1, b2, etc). Each subject should see 3 stimuli, each of the 3 letters and each of the 3 numbers. Yet, the letters and numbers should appear only one time. So for example, one participant will see {a1,b2,c3} and another will see {c1,b3,a2}. But I don't want a participant to see {a3, b2, a1}. There are 36 possible combinations. So of course I can create 36 blocks and display them at random, but I want to avoid this because each stimulus is complicated and errors will occur.

Any idea?