My first thought was to use the MV1815, a chip I had used before.
It needs a 27.75 MHz crystal which is not common.
I got a quote to get them made, for about £140 set-up charge and about 20p per unit. Not impossible but not cheap either.
Googling teletext chips, I found the SDA5273 which seems to be one of the very last - and advanced - chips made before digital TV effectively halted teletext technology.
Suitable DRAM chip:
And 20.48 MHz or 8 MHz crystal, depending on which data sheet you read.
● Single chip teletext IC
● Stores up to 14 teletext pages on chip
● Stores up to 2048 teletext pages with external 16 M memory
● Analog RGB-output
● 41 latin script languages
● 12 × 10 character size
● Parallel display attributes
● 64 from 4096 colors selectable
● Enhanced flash modes
● Dynamically redefinable character set (DRCS, PCS)
● Pixel graphics
● Fullscreen display (64 × 32 or 80 × 24 character positions)
● Horizontal and vertical scrolling
● Graphic cursors
● 4:3 and 16:9 display
● Multinorm display (50/60/100/120 Hz)
● Firmware downloadable
● I2C / 3 wire UART-interface (1 Mbit/s)
● Independent clocks for acquisition and display
● Tools for greatly simplified software development
● 24-Kbyte on-chip reconfigurable DRAM
● 44160-bit character ROM
● One external crystal for all standards
● Analog CVBS-input with on-chip clamping circuitry
● Data Slicer
● Supports level 1, 2.5 and 3.5 ETSI teletext standard
● full level 2.5 processing
At the moment, I'm inclined to use the SAA5246, because it is simple and there is code for it on the web.
I have removed the tuner module (which was dead anyway) to make room for the new circuitry.