They probably come with one or another SAM mod on this site, I just don't remember which, sorry. dds as the rest of the body, since I went through the process I've described recently. On the other hand, I distinctly remember having beast textures with the Schlong integrated on the same. EDIT: I had a doubt so I downloaded the Addon again and it doesn't look like that mod has body textures for the beast races. Sometimes textures are tailored to a specific mesh and switching either just doesn't work. In that case, if Polys are more important than textures, you could consider switching to SAM Light Texture addon (I don't play Argonians so I don't know how different the two texture sets are), and changing the genital texture path in the Creation Kit to the regular body textures. I did this recently when switching from another body to SAM, but I've had several issues with textures not beding correctly around the mesh and creating an awful mess.
If the problem is the mesh you could try taking the schlong mesh from High Poly Body, remove the body, change the slot to 52 and replace the mesh. Low poly mesh or low definition textures?