IMHO the bayonet you guys are looking for would be a typical S98/05 "Butcher-Blade". That being said, there are sub-variants such as the "Aa" (older pattern w/out flashguard, having the wide crossguard "ears" and leather scabbard with metal mounts), or "Na" (newer pattern with flashguard, small "ears" and steel scabbard). Now, add the letter "S" to the equation and this would be the same two variants, but with the sawback-blade. If one uses "abg" in reference to the latter, it would indicate the sawback was officially removed. Lastly, refurbished bayonets abound, and can either be of WW1 or Wiemar/early 3rd Reich period (the latter typically being blued).
If you have a straight, pre-1919 Kar98a, The most common variant would be the S98/05Na. Sawbacks are scarcer and more expensive, as are both the "Aa" patterns. The "abg"s are also becoming more collectible as well. Should your rifle be a Reichwehr reissue, then just about anything would do, but a blued "Na" might be best, and are not as expensive as others. Have attached three pics of my own S98/05s. In the first pic (lower end) are the two earlier variants (with the one at the very bottom a S98/02...the "fore-runner" to the '05). Above that and in pic# 2, are typical S98/05Na, NaS, & a NasAbg. In pic#3 are two Wiemar variants and a S98/05 Ersatz Sawback. Because of poor lighting, had to use the flash, and due to the angle there is a bit of distortion in the photos...