Of course there is.
The same fares are available as before, just renamed 'Thameslink only', or 'Great Northern only' - have you checked a journey planner at all?
Day Save (First Capital Connect)
Was the ticket you're thinking of, but it doesn't appear to be available any more. The new websites make no mention of it and doing a site search returns 0 results.
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He's not talking about ordinary tickets, he's on about the day rover.(used to be valid Bedford-Brighton plus the Wimbledon loop)
The National Rail Enquiries website has a half-updated entry for the Thameslink Daysave ticket. It indicates that the ticket had to be purchased before travel from the Tourist Information Centre in Bedford, Brighton, Dunstable, Greenwich, Luton, Sandy or St Albans. I think that online sales stopped quite a few years ago.