How to find the upper and lower quartiles of the Ryff scale?
Obtaining the quartiles:
Typically you obtain quartiles from the data. Thus, you would have sample data (either your dataset or another dataset), and you can use software to give you .25 and .75 percentiles (or alternatively, you can get such values fairly straightforwardly by rank ordering the data).

Of course, you might be referring to a slightly different notion to quartiles. You might be thinking about low and high scores relative to the scale range. So for example, the mid point of 1 to 5 scale is 3. Therefore, you could say that a mean below 3 suggests that people are below the midpoint on a  scale.
This idea can readily be extended to other percentiles of the scale range.

The basic equation could be expressed as follows:

min + percentile * (max - min) 


where min is the scale minimum and max is the scale maximum and percentile is the percentile of interest (e.g., .25 and .75 in your case or say .5 for the midpoint).

Applying this you get

54 + .25 * (324 - 54) = 121.5
54 + .75 * (324-54) = 256.5


for your low and high cutoffs.

Of course, there's all sorts of discussion you could have about whether this whole process is reasonable, and in general you should try to use the continuous scale for your analyses.