The link to the S&S item did not work. (S&S is a good source for some original and repo Krag items, especially screws and sight parts).

The magazine cut-off from Grandpa's Gunparts is correct. These do show up on ebay and at gun shows and go for about $25. You want the short shaft cut-off for the model 1898/1899 Krag and one that matches the patina of your Krag. (This is a good vendor. You might call and talk to him about your needs).

It appears Schwartz 'retired' for health reasons and does not make hand-guards anymore.
You will probably have to search for an original hand-guard.
Hand-guards are specific to Krag rear sights. A good photo of the various Krag hand-guards can be found on the KCA Website (under 'photos').

Original Krag carbine rear-sights are hard to find and are expensive. You probably want to find a sight before investing in a hand-guard, so you know which hand-guard to get.

The 1901 carbine rear-sight and 1902 carbine rear-sight (5,000) were the ones most used on the model 1899 carbine.

Many of us have used a much cheaper rifle sight as a stopgap. A 1901 rifle sight can be gotten for around $70. Initially, the model 1899 carbine used the same hand-guard as the rifle, with the carbine version of the 1901 sight.

You might contact one of the vendors in the KCA 'classifieds' and see if they have a carbine sight for sale. Also ask about a 'Safety-Lever' (these are also getting hard to find loose and go for about $40-$50).

'Kolhoznik', welcome to the KCA Forum. Some good clear pictures of your 1899 carbine would probably beget more suggestions and advice.