How can I get the currently running kernel version's source ?

[yamada hiroyuki <yamahiroyu_y@yahoo.co.jp>]

Hello,

I built the kernel with debug information for systemtap.
But, systemtap says 

Error inserting module '/tmp/staplTSL5T/stap_c7ba0a7f4c2310db9aea2545f5537756_433.ko': Invalid module format

when insmod is internally called.
I think it is from version conflict between the one currently running and the one I built for debug.
I got the source from the following command.

apt-get source linux-image-$(uname -r)

It seems kernel 2.6.26-25lenny1 is donwloaded.
But running kernel is 2.6.26-21lenny3.
So, I am wondering how I can get 2.6.26-21lenny3 source code.
(I could not find the one on the debian site.)

Also, 2.6.26-21lenny3 is what linux kernel version ?
The dmesg says 

Linux version 2.6.26-2-amd64 (Debian 2.6.26-21lenny3) ...

Is it linux 2.6.26.2 ? 
Could anyone give me a help ?

Thanks in advance,

Hiro