I wasn't sure from your post if you were referring to a .NET Bio implementation/inclusion of a tandem repeat algorithm or more generally if one is available. As to .NET Bio - none currently but the community at large may be investigating something along
those lines. I'll let them comment further.
If you were referring to in general is something available - there is this reference on the web now
http://www.ncbi.nlm.nih.gov/pubmed/9862982 and they note - A World Wide Web server interface atc3.biomath.mssm.edu/trf.html has been established for automated use of the program.