Pretty certain a direct replacement won't be available now, that's an anglian window at least 30 years old, you'd probably need to replace the whole mechanism but that's not a diy job, you'd probably even struggle to get a double glazing service engineer to commit to retro fitting a modern system and get it working properly
Take the window off the hinge and measure the old hinge ideally off the window. Shop around for replacements from window manufacturers. Google comes up with a few suggestions. It will be DIY unless you go for a new window.
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