This is my first post on ikeafans, (Hello from a wet Ireland!

) so forgive me if i'm asking an old question.
Mods, please redirect me if you like.
I'm thinking of using Billy bookcases to fill the alcove each side of the fireplace in my sitting room. The alcoves are 112cm and 117cm each. The wider alcove will also incorporate a tv. I'll probably put the matching doors on too. I'll use extension add-ons and lighting to complete the cabinets to ceiling height.
I was wondering if one can get "fillers" to close the gap between the side of the bookcase and the wall to give a more built-in appearance?
Would it be worth buying an extra bookcase to make fillers out of this?
I've tried looking in other DIY shops for matching veneers, but haven't found anything which will quite match the colour.
Thanks in anticipation etc.
Deadwood.