Hi kenserres,

Here's a nice looking 1898 sight that's currently up for bid/buy-it-now on Gun Broker for $185.00

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You can also look for an 1898 sight at the usual places listed below:

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Like Madesenshooter was alluding to... depending on the type handguard used may determine what model sight will fit. Assuming there is a handguard.

The Model of the rifle/carbine you have will also determine what rear sight would be appropriate.  For example... The Model 1898 could correctly have a 1896, 1898, 1901 or 1902 rear sight mounted.

Pictures would certainly be nice to give us a peek at your beauty!