You can buy a nice one here:
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switch for Glock
A Glock switch enables the shooter to switch between semi-automatic and fully automatic modes, granting them greater control over their shooting experience.
gunswitch.org
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Glock Switch | switch for Glock | Glock switch for sale
The Glock Switch is a unique mechanism that allows firearm owners to enhance the performance of their Glock pistols. Visit our website for more details
penngunshop.com