Here are rational seminormal models of the following Weyl groups. These files are extracted from John Stembridge's Hereditary Models for Weyl Groups. See that page for much more information, including numbering of the representations.
To access John's models directly you need to download and run his Maple program and data files.
For each representation n there is a file Qn or QnCpt. Each matrix is given as a list of n rows. In Qn each row is a list of n entries. In QnCpt it is a list of pairs of numbers; [i,j] means j in the ith place.
For example here is the two--dimensional representation Q2 of W(A2), as a list of 2 2x2 matrices, plus one for the form, in standard format:
ma := [[[1, 0], [0, -1]], [[-1/2, 1/2], [3/2, 1/2]], [[1, 0], [0, 3]]];
Here is the same representation in compact format:
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