Homebrew 2e Magic Items?

Many thanks to everyone within this community that have helped me in the last week. I'm new to 5e but not new to D&D as I've been playing 2e off and on since 1979. However, I've finally taken the plunge to learn 5e and it's definitely been a learning experience. I'm slowly undertaking the art of converting my original 2e character into 5e and have been surprised to find some magic items from the vintage year DM guides aren't available on BDND. In a few instances it was a simple task to recreate the item as a homebrew magic item but for a couple of items it's been a bit more tricky. Specifically, I own a Wand of Negation. First off, is the wand not included in the pick list because it's too overpowered for 5e? If so, I'll just make it disappear and not bring the item forward into this world. Secondly, if it isn't too overpowered is there a way to create a wand that can negate spell-like functions from wands? I was looking through the options the program gives me for special features but I can't find anything that says it as an option. That's what made me think maybe something like that wasn't included when BDND initially created the magic item pick-list because it was too overpowered. Likewise, I had a dagger that was only +2 against fire breathing creatures, but I couldn't find that in the pick-list and the homebrew instructions didn't have a way to designate that characteristic. In that case it couldn't be because it's too overpowered so wondered how I homebrew an item that only affects a targeted species.

Would the alternative be to create the name of item and it's description characteristic but with the understanding that the characteristics aren't actually connected to the BDND program in any way via the electronic character sheet? Instead I would have to just tell the DM that is the item I'm using and a manual die roll would decide if it's successful? For instance, I'm thinking I'll need to do that with Bucknard's Everfull Purse as I can't find that item either. Thanks bunches. 

Thank you for that explanation. I didn't realize that it only had the 5e items. Since I've seen references to other sources I just assumed that everything from historical DMGs made it into the builder. What you've said makes more sense and will help going forward.