Chip paper is rarely on sale on the high street. It is available online at many outlets. For a good selection you will need to search by using several of names ~ butcher ~ fish and chip ~ newsprint ~ packing ~ scrap. If you are on ebay ~ or Amazon ~ or craft-suppliers ~ you will need to check pricing carefully. Size and quantity vary tremendously, and are not always prominently listed. Packs of 100 A4 sheets are convenient, but are rarely good value. Some of these outlets, and also the indivdual sellers, will probably source from their goods from packaging specialists. Although geared for trade sales most are glad for any business. If you are prepared to buy a modest quantity these are probably best value ~ cut out the middleman. Some packaging dealers sell on Amazon and elsewhere.
Carriage can add a lot to orders ~ all paper weighs heavy. As a general rule the packaging specialists and other bulk-dealers charge VAT and carriage separately, and you should check their terms, or click through to carriage costs before confirming the order. Be prepared for cariage charges of £10 or more. Casual bookcrafters will not wish to bulk-buy a lifetime's supply. Small quantities from a crafts supplier may seem cheap, but can be added to other items to avail of carriage paid terms.
I have just made a quick check on Amazon, and found one seller charging twice as much as anyone else, and the sheet size was listed as a quarter of the usual size.
If you do the homework you may well find that the cheapest source of eventual waste paper is an economy pack of A4 office white paper. See it on a good offer and go for it. It really bugs me to have to use it for using it as a paste-overflow-sheet. Maybe I am too fanatical about 'proper tools for the job. If large enough for your needs ~ get some ~ it will be useful for other office duties ~ or even for making notebooks.
Do check the size of sheet you are buying. This type of paper does not follow the ISO "A" sizes (nor any other ISO range). Anyone selling it as A4 will be spending time and money, and possibly waste, cutting it down.
If you have the opportunity, or are prepared to take the trouble, asking your local butcher or chippie if they would order a bundle for you, or maybe just sell a handful. Whenever I have asked I found the staff puzzled at an odd reqest, and hastily suggested the boss handle it (but...'he's not in until tomorrow'). If the boss is reluctant (equals 'cannot be bothered') try asking for his source. He is unlikely to be facing competition by giving away that secret. This all sounds a bit pessimistic, but it is based on recent research that I made before writing this note.
Searching Google for such local suppliers is also difficult. They have many regular clients, making regular purchases, and see no point in paying to have their products listed in the front pages of any search ~ if indeed they even have a web presence. Try 'retailers' supplies'. When I visited the warehouse of one-such, thirty years ago it was an Aladdin's cave of sundries ~ paper bags ~ cellophane bags ~ lollipop sticks ~ string ~ drinking straws ~ sticky tape ~ brown paper. All items bundled by the large boxful ~ by the gross ~ carton of 20 boxes of 500 ~ or anything huge. The local firm used by shops for a wide area around here is called 'Plymouth Agencies'. No clues as to product in that name. I often see their delivery van around, but it is just a box-sided truck.