Make a seperate .PRX that is a kernel one, load it from your usermode .PRX and call an exported function that performs the sceKernelFindModuleByName().
Then return the results back to the calling function in the usermode .PRX
But enumeration in user mode will find only user mode modules (if that is what you want, then all fine). And using sceKernelFindModuleByName in kernel mode and returning the result as it is to user won't help either: it returns a kernel pointer, in the moment user code tries to manipulate it, it would crash, so it is probably better to copy the pointer to a user buffer in the kernel function, unless you only want to check if is NULL or no NULL, in that case, it is fine too :)