To my best knowledge, there is still always an experimental SELEX step involved. Synthesizing random oligo pools is by now probably way cheaper than computationally simulating the folded 3D-structure of tens of thousands of sequences?

But quickly screening the literature on Pubmed brought up some freely accessible articles that could be helpful:

(computer simulation[MeSH Terms]) AND ((Aptamers, Nucleotide[MeSH Terms]) OR (SELEX Aptamer Technique[MeSH Terms]))