I know there is a $\delta$-function representation in terms of the Bessel function as
$$\delta(x-a) = x\int_0^{\infty} t J_{\nu}(xt)J_{\nu}(at)\; dt$$
Is there something similar for
$$\int_0^{\infty} t J_{\mu}(xt)J_{\nu}(at)\; dt$$
Maybe there is something I can do to at least get a reasonable series representation... All I can find are the integrals where the power of $t$ is related in a certain way to the orders $\mu$ and $\nu$, but it is not the case in my case. Thanks!
The integral you seek is null for $\mu\ne\nu$. See the book by Smythe, "Static and dynamic electricity", sections 5.296-5.298.