Kb values of N,N-dimethylaniline derivatives
chemicalize.com is  a cheminformatics website which is the kind of resource you are looking for.

You can use the search tool to find your compounds. The input is the structure itself, which you can draw in-situ.

Here is the $\mathrm{p}K_\mathrm{a}$ data I retrieved from the aforementioned site. Note that these are calculated / estimated, not measured $\mathrm{p}K_\mathrm{a}$ values.



Table 1. $\mathrm{p}K_\mathrm{a}$ values (of the conjugate acid)

$$
\begin{array}{lccccc}
\hline
&amp; 1 &amp; 2 &amp; 3 &amp; 4 &amp; 5 \\
\hline
\textit{ortho-} &amp; 3.71 &amp; 5.19 &amp; -0.98 &amp; 1.44 &amp; 2.66 \\
\textit{meta-} &amp; 3.89 &amp; 5.15 &amp; 1.73 &amp; 4.77 &amp; 3.45 \\
\textit{para-} &amp; 5.55 &amp; 5.46 &amp; 0.65 &amp; 4.68 &amp; 3.65 \\
\hline
\end{array}
$$

Since the question is asking for $K_\mathrm{b}$ values, I converted them too.

Table 2. $K_\mathrm{b}$ values

$$
\begin{array}{lccccc}
\hline
&amp; 1 &amp; 2 &amp; 3 &amp; 4 &amp; 5 \\
\hline
\textit{ortho-} &amp; \pu{5.13e-11} &amp; \pu{1.55e-9} &amp; \pu{1.05e-15} &amp; \pu{2.75e-13} &amp; \pu{4.57e-12} \\
\textit{meta-} &amp; \pu{7.76e-11} &amp; \pu{1.41e-9} &amp; \pu{5.37e-13} &amp; \pu{5.89e-10} &amp; \pu{2.82e-11} \\
\textit{para-} &amp; \pu{3.54e-9} &amp; \pu{2.88e-9} &amp; \pu{4.47e-14} &amp; \pu{4.79e-10} &amp; \pu{4.47e-11} \\
\hline
\end{array}
$$