The closest thing I can think of is something like this:




Search for "Oil & Vinegar Cruet" and you will find a number of interesting shapes that may be of some use. Some of these can make interesting "scientific glassware" for displays and props etc. I have a couple myself...

You could use them 'as is' or possibly modify them slightly (Dremel tool and diamond cutting bits etc), or they are cheap enough to use as a sacrificial object to create a resin mold from...
Another thought: Some bottles of Grappa and similar spirits are available in round bottom long necked bottles - usually the cheaper ones too!
Finally, if you can't find the above, and you just want a smooth round object to make a mold from, you can find cheap scientific glassware, search for "Florence flasks" (also sometimes called "
round bottom boiling flasks") on eBay and other auction sites, these are available in large sizes, though the bigger they are the more they cost. Use a two-part silicone mold to make the master.