If you could describe a little better exactly what you are up against, we might have some suggestions. You haven't mentioned if you are talking about copper, chrome, pvc, etc. Also, is the elbow threaded? Is this elbow part of the trap? Try to come up with a very clear descripion of what is there presently and what the problem is with the present piping.
Mark

A water cooler and a bathroom lavatory are the only two fixtures that are permitted by code to have an 1-1/4" trap & 1-1/4" drain line so it is obvious this question is referring to a bathroom lavatory sink.

Back in the day of cast iron and Gal.iron pipe DWV systems they were also using Galv. iron pipe to run the potable water distribution systems so 1-1/4" pipe was commonly available on the job site.

As iron pipe began to give way to copper or plastic piping materials it soon became apparent that it was inconvenient to maintain a separate inventory of 1-1/4" pipe and fittings solely to install the lavatory waste arms, especially when one considers the limited length permissible with 1-1/4" pipe, by example, the International Residential Code limits a 1-1/4" fixture arm to not more than 5' from the trap weir to the vented stack or branch drain. The Uniform Plumbing Code has reduced that length even more, only permitting a maximum of 2'-6".

Today it is a common practice to fall back on an exception in the code which allows us to increase a trap or drain size by "one nominal trade size" which means that even though 1-1/4" still remains the proper size for a lavatory drain trap and waste arm, nonetheless 1-1/4" pipe is seldom used.

As a consequence as the use of 1-1/4" pipe and fittings fell off it soon became apparent to most hardware and home supply centers that it was just not practical to maintain a full inventory of 1-1/4" DWV fittings however this is beginning to be a real problem for maintenance on existing systems that have the 1-1/4" drain lines. Code expressly prohibits downsizing a line in the direction of flow so we then have two options. 1. Locate the correct 1-1/4" fitting or 2. Change the whole line to 1-1/2".

Over the years I have found that the big box home supply centers have a high volume of the fast moving materials but when it comes down to the real nuts and bolts of the matter, they are rather limited in their selection. If you are looking for the rare or unusual part you will find it much easier in your local neighborhood hardware store. I find that ACE hardware stores generally offer a little bit better selection of plumbing parts than does a True Value hardware, but either one of them have a wealth of material that remains unheard of in the big box stores and if they don't have what you want, in most instances they can get it for you overnight.

The other alternative is to locate a real Plumbing Supply house that will make an over the counter retail sale.