This is the breakdown of the sales by year of the Gameboy officially from Nintendo.
The explanation behind the difference of the numbers you see for every console and for the Gameboy (adding up to 120.4M) and the numbers from their website (adding up to 118.69M) is the following:
There are two types of accounting when it comes to historical recording of their sales: consolidated, and non-consolidated. Non-consolidated sales recording refers to the recording of shipments from Nintendo Co. Ltd.'s domestic inventory in Kyoto, Japan to the inventories of their wholly-owned subsidiaries around the world. These subsidiaries have inventories of Nintendo hardware and software. Normally, Nintendo's subsidiaries inform the corporate office about expected retailer hardware demand, and Nintendo quickly provides them with the inventory to complete a sales transaction. However, until the Nintendo console is shipped to the retailer, Nintendo cannot register it as a "consolidated unit sale." Until then, Nintendo records it as a non-consolidated unit sale. The non-consolidated sales recording method was preferred initially because outside of Japan, NCL could instantly and precisely measure the exact amount of inventory leaving NCL's factories and allocated for sale across the world. Once the subsidiaries had full control over the product, it took a longer period of time for Nintendo Co., Ltd. to receive an exact amount of sales. Nintendo now receives real-time shipment information direct to their corporate offices, so non-consolidated, while still tracked and relevant, isn't as preferred. If you go on Nintendo's website, you can see that Nintendo only provides us with a historical database of consolidated unit sales. However, if you look closely, you can see that Nintendo doesn't disclose Consolidated unit sales prior to 1998. This sales history mixes two sets of data: non-consolidated from 1982 through 2000, and consolidated from 2001 through 2013. They won't disclose old consolidated data, presumably due to reliability issues.
So for the Gameboy we have worldwide numbers:
by march 1990 3.93M
by march 1991 8.06M
by march 1992 10.67M
by march 1993 7.80M
by march 1994 7.47M
by march 1995 5.58M
by march 1996 4.16M
by march 1997 7.09M
by march 1998 11.02M
by march 1999 13.55M
by march 2000 17.24M
by march 2001 18.86M
by march 2002 4.69M
by march 2003 280k
With these numbers we get to 120.4M LT Sales, however to get to the 118.69M number from the consolidated numbers we have to remove a total of 1.71M for the number before march 2000, so 1.71 divided by 11 years gives us that we have to remove around between ~155.45k from every year (although I removed 150 or 160/170k somewhere where needed to be able to give rounded numbers by dozens), so here are the final as close as possible numbers for the Gameboy by year (totalling up to 118.69M):
by march 1990 3.80M
by march 1991 7.90M
by march 1992 10.50M
by march 1993 7.66M
by march 1994 7.30M
by march 1995 5.40M
by march 1996 4.10M
by march 1997 6.90M
by march 1998 10.80M
by march 1999 13.40M
by march 2000 17.10M
by march 2001 18.86M
by march 2002 4.69M
by march 2003 280k
A graph for it would look like this:
