Not sure what IB uses for risk free rates, however, industry standard is to create bootstrap a curve from various sources (LIBOR, futures, Swaps). This is how the Bloomberg Terminal creates their RFR curve for default option pricing.?
A decent alternative is just to pull treasury par yields from the??(they also have an XML public API), bootstrap a zero coupon curve from these rates, and finally interpolate on this curve for the given maturity of your the options being modeled.?
You will find, however, that rates are almost meaningless for many options, especially those with less than 6 months maturity. Depending on your product of choice, arguably a more important input than rates is a decently accurate, forward-looking dividend rate ?(discrete or continuous).?
